Postpartum Anestrus Research Articles

Effect of supplementation with corn oil on postpartum ovarian activity, pregnancy rate, and serum concentration of progesterone and lipid metabolites in F1 (Bos taurus × Bos indicus) cows

The aim was to evaluate the effect of corn oil supplementation during postpartum anoestrus on ovarian activity, pregnancy rate, progesterone (P(4)), and lipid metabolites (cholesterol, CHO; low and high density lipoproteins; LDL and HDL, respectively) concentrations in blood of F(1) (Bos taurus x Bos indicus) grazing cows. Cows were randomly assigned to an experimental group, fed with a supplement containing 4% corn oil on dry matter basis (OG, n = 11), and a control group with the same supplement without corn oil (CG, n = 12). Both supplements contained equivalent amounts of crude protein and metabolizable energy and were fed for 34 days continuously. All cows were induced to estrous 12 days after beginning of supplementation by using a synthetic progestagen and artificially inseminated 56 h after retiring the implants. Pregnancy diagnosis was performed by transrectal palpation 45 days after insemination, evaluating simultaneously ovarian activity. P(4) and lipid metabolites (CHO, HDL, LDL) concentrations were determined in blood samples collected at 3-day intervals, from the beginning of corn oil supplementation and up to 10 days after artificial insemination. Ovarian activity was affected by treatment (p < 0.05), finding ovarian structures in 72.7% of OG cows and in 50% of CG cows. Concentration of P(4) and CHO was higher for OG with respect to CG (2.52 +/- 0.65 vs 1.88 +/- 0.62 ng/ml and 117.79 +/- 11.57 vs 85.71 +/- 12.11 mg/dl, respectively), whereas pregnancy rate and blood concentrations of HDL and LDL were not affected by treatment (p > 0.05). Addition of corn oil to the supplement stimulated ovarian activity and increased serum concentrations of progesterone and cholesterol in grazing B. taurus x B. indicus cows with low body condition score showing postpartum anoestrus.

Flushing em vacas de corte no pós-parto, submetidas ao desmame precoce: desempenho reprodutivo

The objective of this experiment was to evaluate the effects of short-time fat supple-mentation (flushing) on the reproductive performance (postpartum estrus, postpartum anestrus, postpartum estrus interval, calving interval, number of artificial insemination, artificial insemination interval, and pregnancy rate) of postpartum beef cows, submitted to the early weaning. Two hundred and fifty eight beef cows were used from the following genetic groups: Aberdeen Angus (n= 21), Aberdeen Angus x Canchim (n= 20), Canchim x Aberdeen Angus (n= 52), Charoles x Caracu (n= 29), Charolais (n= 18), Cachim (n= 34), Caracu (n= 35), Caracu x Charoles (n= 26) an Puruna (n= 23), with 418.1 kg of body weight and all pregnant. These animals were split into two types of treatments: flushing (30% soybean full + 70% corn) and no supplementation. There was no flushing effect on postpartum estrus percentage (82.9%), anestrus percentage (17.0%), postpartum estrus interval (100.5 days), calf birth weight (34.2 kg), number of artificial insemination (1.4), interval between the 1st and the 2nd artificial insemination (19.2 days), interval between the 1st and the 2nd artificial insemination (19.9 days), and pregnancy percentage (54.6%). The flushing reduced calving interval (391.14 vs. 399.31 days). The November period had lower postpartum estrus percentage (70.6%), anestrus percentage (29.4%), postpartum estrus interval (90.3 days), calving interval (378.3 days), number of artificial insemination (1.2), interval between the 1st and the 2nd artificial insemination (11.5 days), and pregnancy percentage (27.5%).

Effects of nursing frequency and parity on the productive, metabolic and reproductive parameters of beef cows

Nursing restriction and parity might be stressful factors influencing the challenging post-partum period. This experiment aimed to evaluate the effects of nursing frequency (in multiparous dams) and parity on faecal glucocorticoid metabolites after calving in beef cows ( n = 64). Also, the role of these effects on productive, metabolic and reproductive functions was assessed. From the day after calving, forty-six Parda de Montaña cows were assigned at random to three nursing frequencies: once-daily nursing (1 × 30 min at 0800 h) (RESTR1), twice-daily nursing (2 × 30 min at 0800 and 1530 h) (RESTR2) and ad libitum nursing (ADLIBC). Eighteen heifers were maintained with free access to their calves as in the ADLIB cow's group (ADLIBH). Data were analysed through analysis of variance and survival analysis. The faecal glucocorticoid metabolites during the first three days post-partum were not affected by either calf management or parity ( P > 0.10) but they were greater at 12 h post-partum than in subsequent samplings ( P < 0.05). Cow average daily gain (ADG) was greater in RESTR1 than in RESTR2 and ADLIBC ( P < 0.05). However, milk yield and calf ADG were lower in RESTR1 than in the rest (P < 0.05). These traits did not differ between parities ( P > 0.10). Serum triglycerides and urea were not affected by calf management or parity ( P > 0.10). Peripheral cholesterol and IGF-I did not differ among suckling systems ( P > 0.10), but their mean concentration was lower in ADLIBC than in ADLIBH ( P < 0.05). Serum NEFA was lower in RESTR1 than in RESTR2 and ADLIBC on weeks 7 and 9 of lactation ( P < 0.05). Both RESTR1 and RESTR2 treatments showed lower serum NEFA than ADLIBC on week 11 post-partum ( P < 0.05). Serum NEFA were greater in ADLIBC than in ADLIBH on week 1 and after week 7 of lactation ( P < 0.05). Serum β-hydroxybutyrate was lower in RESTR1 and RESTR2 than in ADLIBC ( P < 0.05). Calf management did not affect significantly the interval to first post-partum ovulation or oestrus ( P > 0.10) but ADLIBC had shorter post-partum intervals to first ovulation than ADLIBH ( P < 0.05). In conclusion, calf restriction and parity were factors that did not affect cow's welfare after parturition. Twice-daily and ad libitum suckled cows showed a similar productive and metabolic behaviour which differ from their once-daily suckled counterparts. This response did not trigger remarkable differences in the reproductive parameters of cows. Ad libitum suckled cows had different metabolic traits compared to heifers, as well as a shorter duration of the post-partum anoestrus than ad libitum suckled first-calf dams.

Recent Advances in the Synchronization of Estrus and Ovulation in Dairy Cows

Synchronization programs have become standard components in the current breeding management of cows in the dairy herds of most dairy industries. Many are based on protocols that allow timed inseminations (TAI) so as to circumvent the practical difficulties associated with estrus detection. These difficulties are exacerbated in modern herds of high producing cows either because of increasing herd size in which individual animal monitoring is difficult and often subjective, or because small intensively managed herds are milked in robotic systems that minimize animal: staff interactions. Additional reasons arise from high producing cows having less obvious symptoms of estrus, partly because of housing systems combined with intensive feeding and milking, partly because of higher metabolic clearance rates of reproductive hormones like estradiol and partly because of the increasing prevalence of prolonged post-partum anestrus and reproductive tract pathology. The most recently developed programs include protocols for resynchronization following first or subsequent inseminations. These re-synchronization protocols may involve selected forms of hormonal intervention during the diestrous and pro-estrous periods following TAI, or following pregnancy diagnosis by ultrasound from 28 days after TAI. The latter form of re-synchronization has become increasingly important with the recognition that late embryonic/early foetal death has become a major factor compromising the reproductive performance of high producing Holstein cows in many dairy industries. Although cows detected in estrus without any hormonal treatment before insemination have higher conception rates than those inseminated following synchronization and TAI, the low detection rates combined with embryonic death means that intervals from calving to conception (days open) are usually less when synchronization programs have been successfully implemented. One of the significant factors affecting a program's success is the compliance rate that may sometimes be less than 70%. Almost all programs involve strategically timed injections of prostaglandin F2alpha (PGF) and gonadotropin releasing hormone (GnRH). Injections of an estradiol ester and progesterone supplementation per vaginum may be included in some programs. The basic program is the "Ovsynch" regimen. Numerous variations have been tested and developed. Many involve increasingly complex protocols that increase the risk of non-compliance, none has consistently achieved conception rates that exceed 40% and few have reduced the incidence of embryonic death. These synchronization programs are the best that are currently available. They have not been able to overcome the consequences of lowered fertility associated with high levels of milk yield, forms of nutrition and environmental factors like heat stress that have profound effects on the physiology and metabolism of the high producing dairy cow.

Endocrine patterns of the estrous cycle and pregnancy of wildebeest in the Serengeti ecosystem

Despite the importance of the western white-bearded wildebeest ( Connochaetes taurinus mearnsi) to the Serengeti–Mara ecosystem, surprisingly little is known about the reproductive physiology of this keystone species. A longitudinal, non-invasive endocrine study was conducted on female wildebeest captured from the Serengeti–Mara migration and maintained for ∼16 months in large fenced enclosures within the species’ natural range. An intact bull was introduced to a female subgroup ( n = 5), while remaining females ( n = 10) were unexposed to a male. Fecal progestagen patterns reflected ovarian activity and pregnancy. In non-pregnant animals, luteal and inter-luteal baseline progestagen values differed ( p < 0.001) over time, thereby allowing identification of recurrent estrous cycles. The average durations of the luteal phase, estrous cycle, gestation, and post-partum anestrus were 14.3 ± 0.5, 22.6 ± 1.0, 240.8 ± 11.7, and 104.1 ± 15.6 d, respectively. Annual reproductive patterns indicated a distinctive period of ovarian activity that extended from 13 May through 3 December (203.5 ± 29.9 d) with all unmated females displaying from one to 14 estrous cycles. Progestagens were higher ( p < 0.001) in pregnant ( n = 4) than non-pregnant ( n = 10) cows. These data (1) reveal the value of fecal hormone monitoring for establishing the first ever endocrine profiles of female wildebeest in semi-free-living conditions in their native range, and (2) indicate that the species is a seasonal breeder that is polyestrous and a spontaneous ovulator.

132 INDUCTION OF FIRST POSTPARTUM OVULATION AFTER ADMINISTRATION OF GnRH, ESTRADIOL BENZOATE, OR LH ASSOCIATED OR NOT WITH CALF REMOVAL IN NELORE COWS

There are reports in the literature indicating that the presence of calf, body condition score, energy balance, number of births (multiparous v. primiparous), and breed are factors that influence the duration of postpartum anoestrus in beef cows. The purpose of the present study was to evaluate, during early postpartum, the time necessary for reestablishment of pituitary LH stocks, determined by the hypothalamic-pituitary axis responsiveness to exogenous administration of GnRH and estradiol benzoate (EB). Multiparous lactating Nelore cows (n = 51) were kept in Brachiaria brizantha pasture. The animals were randomly allocated in 8 groups, according to the hormonal treatment: EB Group (1.0 mg of EB, i.m. Estrogin®, Farmavet, Sao Paulo, Brazil; n = 7), EB and calf removal (CR) group (EB/CR, calves were removed at the time of birth, n = 4), EB/SUP group (cows were supplemented with a balanced diet, based on cotton meal and ground corn, from the beginning of the experiment until ovulation), GnRH group (100 μg, licereline, i.m. Gestran Plus®, ARSA SLR, Buenos Aires, Argentina; n = 7), GnRH/CR group (n = 4), GnRH/SUP group (n = 8), LH group (12.5 mg, i.m. Lutropin® Bioniche, Ontario, Canada; n = 7), and control group (did not receive any hormone to induce ovulation or diet supplementation, n = 5).The hormones were administered weekly, from 7 days postpartum (±5 days) until the occurrence of the first ovulation, which was determined by the presence of CL during weekly ovarian ultrasonography (Aloka 900, Tokyo, Japan, 7.5 MHz probe). The data were analyzed by ANOVA. On average (±SEM) the first ovulation occurred 86.7 ± 0.5 (EB); 19.7 ± 0.6 (EB/CR); 57.8 ± 0.4 (EB/SUP); 44.7 ± 0.5 (GnRH); 25.9 ± 0.6 (GnRH/CR); 32.8 ± 0.4 (GnRB/SUP); 42.4 ± 0.5 (LH); and 59.3 ± 0.5 (control) days postpartum. There were significant differences between groups: EB v. EB/SUP (P &lt; 0.01), EB v. EB/CR (P &lt; 0.01), EB v. control (P &lt; 0.04), EB v. GnRH (P = 0.01), and there was a tendency between groups: GnRH v. GnRH-SUP (P = 0.10) and LH v. control (P = 0.10). The first ovulations were detected from the second week postpartum (animals from Groups GnRH and EB/CR) until the last ultrasound examination on Day 120 postpartum (Group EB). The results indicate that from the second week postpartum there is sufficient LH in the pituitary to induce ovulation after GnRH or EB administration. However, the cows from EB group ovulated later than animals from the other groups, possibly due to the sensitivity of hypothalamus to negative feedback of estrogens, inhibiting the pre-ovulatory LH surge. Additionally, calf removal and food supplementation reduced in 2 to 4 weeks the time of the first postpartum ovulation induced by GnRH or EB. Fellowship from FAPESP. Supported from FAPESP (Sao Paulo, Brazil).

217 EFFECT OF FREQUENCY OF MILKING ON POSTPARTUM EVENTS IN SISTANI CATTLE

Prolonged postpartum anestrus is a major concern in Bos indicus breeds. Sistani cattle is an Iranian Bos indicus beef breed with more than 5000 years of history in the northwest part of Iran, Sistan. This breed is well adapted to the harsh, arid environment, which includes 120 days of hot winds. Small holders in the Sistan region use Sistani cattle for both meat and milk. The purpose of this study was to investigate the effect of frequency of milking on the postpartum events in this breed. Healthy Sistani cattle (n = 41) with 3.3 ± 0.3 parity and normal parturition were randomly assigned to 3 groups after parturition and were monitored for 3 months. Cows in Groups 1 and 2 were milked once (n = 15) or twice (n = 14) per day, respectively. The control (n = 12) cows were not milked. All cows were allowed to be suckled by their calves once per day. Throughout the 3 months of monitoring after calving, blood samples were collected weekly and assayed for progesterone using RIA. Standing estrus was detected every day at 0700, 1400, and 2100 h. The first rise in progesterone after calving was considered when it was above 1.5 ng/mL. Data were analyzed using GLM procedure in SAS (SAS Institute, Cary, NC). There was no significant difference in the variables measured among groups (P &gt; 0.05); therefore, the data were pooled (Table 1). The number of estrus, the day of the first estrus, and the first rise in progesterone after calving were 2.9 ± 1.42, 31.2 ± 1.77, and 38.8 ± 2.20, respectively (Table 1). Average number of service per conception (1.6 ± 0.12) and days open (94.4 ± 7.63) in Sistani cattle may be considered to be superior reproductive indices to those reported in the majority of Bos indicus breeds. In conclusion, once-daily or twice-daily milking did not influence postpartum reproductive indices of Sistani cattle, indicating that twice-daily milking may be advised to enhance the profitability of small holders. In Sistani cattle, ovarian activity and estrous behavior resumed fairly soon after partition, allowing for earlier conception in this breeds. Table 1.Postpartum reproductive indices of Sistani cattle with varying frequencies of milking This research was funded by the Research Deputy of the University of Tehran and Animal Science Research Institute.

Effect of restricted suckling on milk yield, composition and flow, udder health, and postpartum anoestrus in grazing Holstein cows

The effect of restricted suckling on milk yield and composition, udder health, and postpartum anoestrus in dairy cows in pasture-based systems, was studied in 32 Holstein multiparous cows and their calves. At calving, each cow–calf pair was randomly assigned to one of two treatments: restricted suckling (RS) of the cows by her own or another calf, twice daily for 30 min or artificial rearing (AR) of the calves with milk obtained from the bulk tank, offered twice a day in buckets. Treatments were applied until week 8 after calving. The diet of the cows consisted of direct grazing in improved pastures, corn silage and a commercial concentrate which was offered at milking. Milk production and composition, udder health, body condition score of the cows, body weight and milk intake of the calves were measured weekly, and the first postpartum ovulation was determined three times a week by ovarian ultrasonography. Cows with RS management had a lower machine-milked milk yield (17.9 vs. 24.8 kg/d), a lower fat percentage (3.21 vs. 4.11%) and 4% fat-corrected milk yield (16.2 vs. 25.7 kg/d), and also a lower average milk flow (1.35 vs. 1.76 kg/min) than cows in the AR treatment. There was no effect of treatment on milk protein percentage or udder health as measured by milk electrical conductivity. The interval from calving to first postpartum ovulation was shorter in the AR cows than in the RS cows (18.5 vs. 21.8 days). The RS calves consumed more milk (7.2 vs. 5.4 kg/d), gained more body weight (0.813 vs. 0.656 kg/d), and had a higher body weight at weaning (84.3 vs. 73.3 kg) than AR calves. Restricted suckling of grazing dairy cows had a negative effect on machine-milked milk yield, fat percentage and 4% fat-corrected milk yield, but had no effect on udder health or on improved weight gain and body weight at weaning of the calves.

Duration of daily bull exposure on resumption of ovulatory activity in postpartum, primiparous, suckled, beef cows

The objective of this experiment was to determine if duration of daily bull exposure influences length of postpartum anestrus in primiparous, anovular, suckled, beef cows. The null hypotheses were that intervals from calving or the start of bull exposure (D 0) to resumption of ovulatory activity (OA), and proportions of cows that resumed OA during the experiment does not differ among cows exposed to bulls for 0 h, 6 h, or 12 h daily, and that there is no relationship between the duration of bull exposure and interval to resumption of OA in cows exposed to bulls for 0 h, 6 h, or 12 h daily. At 51.5 ± 2.3 d (±SE) after calving, cows were assigned randomly to be exposed for 12 h (BE12; n = 15) or 6 h daily (BE6; n = 14) to bulls, or not exposed to bulls (NE; n = 10) for 45 d. Interval from calving or from D 0 to resumption of OA was shorter ( P < 0.05) and the proportion of cows that resumed OA during the experiment was greater ( P < 0.05) for BE12 than for NE cows. Interval from D 0 to resumption of OA did not differ ( P > 0.10) between BE6 cows and either BE12 or NE cows. However, interval from calving to resumption of OA was shorter ( P < 0.05) for BE6 than NE cows. The proportion of cows that resumed OA did not differ ( P > 0.10) between BE6 cows and BE12 cows; however, the proportion of cows that resumed OA during the experiment tended ( P = 0.08) to be greater for BE6 cows than for NE cows. There was a linear relationship between intervals from calving ( b 1 = −7.64 d/h; P < 0.05) and D 0 (b 1 = −3.3 d/h; P < 0.05) to resumption of OA and duration of daily bull exposure. Thus, the duration of bull-pheromone stimuli that cows perceive each day is related to when primiparous, postpartum, anestrous, suckled cows respond to this stimulus and undergo the physiological changes necessary to resume ovulatory activity.

Postpartum anestrus in cows

The study was conducted on 70 cows of Friesian and Holstein breed in AL-Faihaa station, Babylon Governorate during the period from January 2002 to March 2002. The age of animals ranged between 2 to 7 years. The study was designed to know the prevalence of postpartum anestrus and their treatments in cows. The prevalence of postpartum anestrus was 51.42% (36/70). The animals suffering from persistent corpus luteum were showed an incidence of 38.88% (14/36). The animals were treated with 15 mg PGF2α i.m. The animals suffering from inactive ovaries were showed an incidence of 61.11% (22/36). The animals suffered from inactive ovaries (n = 22) were divided into three groups; the first group (n = 9) were treated with 50 ml Lugol’s Iodine solution 5% intra uterine; The second group (n = 6) were treated with 0.5 mg GnRH i.m. while the third group (n = 7) treated with 6 mg estradiol benzoate i.m. The efficiency of the treatments were 55.5% , 100% and 71.4% respectively. There was a significant difference (P< 0.05) between different groups. It was concluded from this study that the postpartum anestrus prevalence is high and could be treated with PGF2α or GnRH with high success rate.

92 INDUCTION OF FIRST POSTPARTUM OVULATION, AFTER ADMINISTRATION OF GONADOTROPIN-RELEASING HORMONE OR ESTRADIOL BENZOATE, IN NELLORE COWS

There are reports in the literature indicating that the presence of calf, body condition score, number of births (multiparous v. primiparous), and breed are factors that influence the duration of postpartum anestrus in beef cows. The purpose of the present study was to evaluate, during early postpartum, the time of the reestablishment of LH stocks, measured by the hypothalamic-pituitary axis responsiveness to exogenous administration of gonadotropin-releasing hormone (GnRH) or estradiol benzoate (EB). Primiparous lactating Nellore cows (n = 38, body condition score 2.5 to 3.5, on a 0 to 5 scale) were kept in a Brachiaria brizantha pasture. The animals were randomly allocated into 2 groups, according to hormone treatment: EB group (1 mg EB, i.m., Estrogin®, Farmavet, Sao Paulo, Brazil; n = 20) and GnRH group (100 μg, licerelina, i.m, Gestran Plus®, ARSA S.L.R., Buenos Aires, Argentina; n = 18). In each group, half of the animals were supplemented with a balanced diet based on cotton meal and ground corn. The drugs were administered from 7 days postpartum (±4 days), at intervals of 7 days, until the occurrence of the first ovulation that was observed by weekly ultrasonography (US, Aloka 900, Tokyo, Japan; 7.5-MHz transrectal probe). The data were analyzed by ANOVA (Proc GLM, SAS Institute, Cary, NC). Within the GnRH and EB groups, the first ovulation occurred 15 and 33 days postpartum, respectively, whereas the group averages (± SD) occurred earlier in cows treated with GnRH compared with those treated with EB (43.0 ± 3.8. v. 75.1 ± 8.7 days postpartum, respectively; P &lt; 0.01). In the EB group, 4 animals did not ovulate until Day 140 postpartum. There was no interaction of treatment (GnRH, EB) × nutrition (supplemented, nonsupplemented). When data from the EB and GnRH groups were combined, there was a significant difference between supplemented and nonsupplemented animals (44.4 ± 6.2 v. 68.9 ± 7.3 days, respectively; P &lt; 0.02). The results indicate that GnRH induces ovulation from Day 15 postpartum, suggesting the presence of sufficient LH in the pituitary to induce the first ovulation at this time. However, EB administration did not induce ovulation in this period, possibly because of the sensitivity of the hypothalamus to negative feedback of estrogens, inhibiting the preovulatory LH surge. These results also indicate that nutritional supplementation anticipates the first postpartum ovulation induced by GnRH or EB. Support by FAPESP(Sao Paulo, Brazil); fellowship from FAPESPA; fellowship from CAPESB.

RESEARCHES REGARDING INCIDENCE, DIAGNOSIS AND THERAPY OF GENITAL DISORDERS IN DAIRY COWS

The study was realised on 113 Holstein Friza cows from S.C.SARIS COM 96 S.R.L., in order to establish the incidence of reproductive disorders in post-partum period and of infertility and also to elaborate an adequate therapy. From the 113 dairy cows examined, retained placenta was diagnosed in 4 cases (3%). One of the cows developed a purulent endometritis, which has been diagnosed based on the inspection and transrectal examination. Infertility was diagnosed in 27 cows, which presented a prolonged post-partum anestrus. Case history, ultrasonography and hormonal determinations were used to establish the right diagnosis – ovarian hypolasia in 18 cows (66.6%), persistent corpus luteum in 5 cows (18.6%) and ovarian cysts in 4 cows (14.8%). The therapy of retained placenta was based on the administration of PGF2alfa at 24 hours post-partum, combined with the local therapy (5g oxitetracycline, 30ml alchool 40°, 500ml NaCl 0.9%). The therapy of infertility was succesfull in 80% of cases, 22 cows from the 27 with infertility problems returning to heat.

Energy Balance and Reproduction on Dairy Cows Fed to Achieve Low or High Milk Production on a Pasture-Based System

This study investigated the energy balance, metabolic changes, reproduction, and health in Australian Holstein-Friesian cows of average genetic merit fed to produce 6,000L of milk/cow per lactation (restricted production; Rp) on a predominantly grazed pasture diet, or 9,000L of milk/cow per lactation (high production: Hp) on a more intensive feeding regimen by using a partial mixed ration to supplement pasture. The mean 4% fat-corrected milk (FCM) and standard deviation achieved was 8,466±1,162L/cow per lactation for the Hp herd and 6,748±787L/cow per lactation for the Rp herd. During early lactation, the degree of estimated negative energy balance was less in the Hp cows than in the Rp cows (−16.1 vs. −29.1MJ/cow per day, respectively). Consequently, the mobilization of body reserves was also lower in the Hp cows, and this was reflected in lower concentrations of nonesterified fatty acids (0.70 vs. 0.84mmol/L) and β-hydroxybutyrate (0.51 vs. 0.69mmol/L) and greater concentrations of glucose (3.51 vs. 3.34mmol/L) and insulin-like growth factor-I (78.9 vs. 58.7ng/mL) for Hp and Rp cows, respectively. After calving, body condition score and body weight decreased to a similar extent in both herds and did not reflect the differences in mobilization of body reserves between the 2 herds. Reproductive performance was not significantly related to level of milk yield. The mean interval from calving to first active corpus luteum was 33 (SD=20) d postpartum, and there were 1.4 (SD=0.8) estrus cycles before the beginning of the breeding period (>50d postpartum). The interval from calving to pregnancy was 114d, and the pregnancy rate after 12 wk of mating was 74%. The number of cows with ovarian abnormalities was also similar between the 2 herds. Cows with a long postpartum anestrus had the lowest concentration of insulin-like growth factor-I. The number of health-related disorders was also similar between the herds, with the exception of mastitis, for which the incidence was significantly greater in the Hp cows. The results indicate that the production per cow could be increased from 6,748L of FCM/cow per lactation for cows grazing pasture and supplemented with concentrates only at milking to 8,466L of FCM/cow per lactation, in one lactation, by supplementing pasture with a partial mixed ration. Despite the fact that production per cow increased substantially, the degree of estimated negative energy balance and the metabolic changes in early lactation were lower and reproductive performance was maintained.

Effect of Prepartum Energetic Supplementation on Productive and Reproductive Characteristics, and Metabolic and Hormonal Profiles in Dairy Cows under Grazing Conditions

The effect of cracked corn grain supplementation (3.5 kg/day) during 3 weeks before the expected calving date on milk production and composition, body condition score (BCS), metabolic and hormonal profiles and length of postpartum anoestrus was evaluated in multiparous Holstein dairy cows under grazing conditions (Energy supplemented group, n = 10; Control group, n = 10). Body condition score was weekly recorded during the peripartum period, from days -21 to +35 (parturition = day 0). Non-esterified fatty acids, beta-hydroxybutyrate, cholesterol, urea, insulin, insulin-like growth factor I (IGF-I), leptin, thyroxine (T(4)) and 3,3''5-triiodothyroinine (T(3)) were weekly determined in plasma from days -21 to +35. The reinitiation of ovarian cyclicity was twice weekly determined by ovarian ultrasonography and confirmed by plasma progesterone concentrations. Cows fed energy concentrate prepartum had higher BCS during the prepartum and postpartum and produced more milk. Non-esterified fatty acids plasma concentrations were significantly higher in the energy group, while cholesterol was higher in the control group. Treated cows had higher levels of plasma insulin, IGF-I and leptin pre-calving. IGF-I, leptin and T(4) were diminished during the early postpartum period in both groups. Insulin levels were also diminished in the control group, but levels remained high in the energy-supplemented group. Treated cows ovulated sooner after parturition than controls. We conclude that Energetic supplementation prepartum in cows under grazing conditions increased milk production and reduced the reinitiation of ovarian activity, consistent with a better EB (BCS), higher prepartum levels of IGF-I, leptin and insulin, and higher insulin levels during early postpartum.

The Importance of Interactions Among Nutrition, Seasonality and Socio‐sexual Factors in the Development of Hormone‐free Methods for Controlling Fertility

Around the world, consumers are demanding animal products that are produced to agreed standards for human health, environmental management and animal welfare. This has led to the development in Australia of the concept of 'clean, green and ethical' (CGE) animal production based on the manipulation of nutrition ('focus feeding') and the application of phenomena, such as the 'male effect', to provide 'natural' methods for managing small ruminant production systems. With respect to the management of fertility, CGE involves utilization of the inherited responses of animals to environmental factors to manipulate their reproductive processes. The successful development and implementation of this new generation of management tools depends on a thorough yet holistic understanding of the interactions among environmental factors and the ways these interactions affect reproductive physiology and behaviour of the animal. For sheep and goats, a central aspect of CGE management is the way in which ovarian function is affected by three major factors (nutrition, photoperiod and socio-sexual signals) and by interactions among them. Nutrition can exert two profound yet contrasting types of effect on ovarian activity: (i) the complete inhibition of reproduction by undernutrition through the hypothalamic mechanism that controls ovulation and (ii) the enhancement of fecundity by nutritional supplementation, through a direct ovarian mechanism, in females that are already ovulating. A similarly profound control over ovarian function in female sheep and goats is exerted by the well-known endocrine responses to photoperiod (seasonality) and to male socio-sexual signals. The 'male effect' already has a long history as a valuable technique for inducing a synchronized fertile ovulation during seasonal and post-partum anoestrus in sheep and goats. Importantly, experimentation has shown that these three major environmental factors interact, synergistically and antagonistically, but the precise nature of these interactions and their significance to reproductive outcomes are not well understood. Most research to date has been with small ruminants but CGE principles can be applied to any species in a managed environment. For example, a male effect has been reported for lactating cattle and, in the horse, the pattern of seasonality of oestrus can be altered by nutrition. Well-fed mares have a longer breeding season and some animals become non-seasonal. Similar observations have been reported for sheep and goats. By working towards a holistic perspective of the physiology, nutrition, genetics and behaviour of our animals, we will be able to formulate ways to manipulate the animals' environment that will improve management, productivity and profitability and, simultaneously, promote a CGE industry.

Effect of Restricted Feeding and Monopropylene Glycol Postpartum on Metabolic Hormones and Postpartum Anestrus in Grazing Dairy Heifers

This study was designed to determine the effects of feed restriction and monopropylene glycol (MPG) supplementation on the reproductive, milk production, and somatotropic axes in dairy heifers postpartum. At calving, 49 Holstein-Friesian heifers were allowed either unrestricted (UNR; n=18) or restricted access to pasture with (RES+MPG; n=13) or without (RES; n=18) MPG supplementation (250mL drenched twice daily for 150 d). The average body condition score (BCS) of the heifers was 5.3±0.2 on a scale from 1 to 10 (where 1 = emaciated and 10 = obese). Body condition score and body weight were similar among the groups at calving and decreased after calving for all groups. However, body weight loss was around 10% greater for the RES and RES+MPG groups from wk 3 to 12 compared with UNR group. The length of the postpartum anestrous interval was similar for all groups (47, 51, and 45±5 d for the UNR, RES, and RES+MPG, respectively). Average milk production, protein, fat, and lactose yields during the first 12 wk postpartum were greater in the UNR group than in the RES and RES+MPG groups. Feed restriction affected plasma concentrations of insulin, with lower concentrations in the RES group compared with the UNR group. There were no differences in plasma concentrations of insulin between the RES+MPG group and the UNR or RES groups. An effect of feed restriction was observed on insulin-like growth factor-I concentrations and also a treatment by time interaction with a changing pattern through time as concentrations in the UNR group increased relative to the RES and RES+MPG groups. There were no differences in growth hormone concentrations among the groups. Glucose concentrations were lower in the RES group when compared with RES+MPG and UNR groups and this difference lessened over time. Plasma concentrations of nonesterified fatty acids were greater in the RES group compared with the RES+MPG and UNR groups. Leptin concentrations in the UNR group were greater than in the RES and RES+MPG groups. Hepatic growth hormone receptor 1A, total growth hormone receptor, and insulin-like growth factor-I relative mRNA expressions decreased postpartum with no effect of feed restriction, MPG supplementation, or interaction between time and treatment. During a challenge with MPG, insulin secretion was stimulated but no effect on postpartum anestrous interval in the treatment groups was observed. It was concluded that restricted pasture availability postpartum in dairy heifers calving in optimal BCS had no effect on the postpartum anestrous interval. It did however decrease milk production; thus, we can infer that monopropylene glycol supplementation does not act to prevent loss of milk yield.

Weekly bull exchange shortens postpartum anestrus in suckled beef cows

The duration of anestrus in cattle was usually shortened when cows were exposed to bulls. The objective of the present experiment was to determine if weekly bull exchange accelerated the resumption of cyclicity in postpartum suckled beef cows. We tested the hypothesis that exposure of postpartum, anestrous, suckled beef cows (extensively managed) to weekly exchange of bulls, accelerates the resumption of cyclicity, compared to continuous exposure to the same bulls. Ninety-one multiparous suckled Hereford and Hereford x Angus cows, <60d postpartum, were assigned to two homogeneous groups. Beginning on December 1st (late spring), the control group (C, n=45) remained with one pair of bulls throughout the breeding period (7 weeks), whereas in the "exchanged" (E, n=46) group two pairs of bulls were exchanged weekly. Based on weekly ultrasonographic examinations of all cows, none had a CL at the start of the experiment and for 2 weeks after the start of bull exposure. However, the accumulated frequency of cows with a CL was greater in group E than in group C cows on week 4 (P=0.024), as well as on weeks 5-7 (P<0.001) after the start of bull exposure. Furthermore, in group E versus group C, there was a higher pregnancy rate 30d after the end of bull exposure (26 of 46, 56.2% vs. 16 of 45, 35.6%; P=0.045). In conclusion, weekly exchange of two pairs of bulls shortened postpartum anestrus in suckled multiparous cows, compared to continuous exposure to a single pair of bulls.

Fertility of Zero-Grazed Dairy Cattle following Hormone Treatment and Fixed-Time Artificial Insemination

Reproduction is important to dairy herds and achievement of economically optimal performance still remains a substantial multifactorial challenge in many herds. Poor estrus expression and detection, repeat breeding, prolonged postpartum anestrus and delayed onset of puberty are some of the limiting factors to attainment of optimum reproductive efficiency in zero-grazed herds. This study investigated the fertility of anestrous and repeat breeder zerograzed dairy animals following induction of ovarian cyclicity, synchronization of ovulation, and fixed time insemination. The following three categories of animals were recruited into the study: 1) Delayed puberty or anestrus in heifers (n=26), 2) Prolonged postpartum anestrus (n=23), and 3) Repeat breeding cows and heifers (n=28). The seventy seven animals (69 Friesians, 7 Ayrshires and 1 Guernsey) were all zero-grazed and had a median age and parity of 5.0 years and 2.5 respectively, and a body condition score of at least 2.5 on a scale of 1 to 5. All study animals were intramuscularly injected with Gonadotropin Releasing Hormone (GnRH) on Day 0, Prostaglandin F2&#945; (PGF2&#945;) on Day 7, and GnRH on Day 9. Treated animals had timed artificial insemination (AI) 8-24 hours after the last injection. Pregnancy diagnosis was performed by rectal palpation 60 days post-AI. The pregnancy rate for anestrous cows (6/23) was 26.1%, repeat breeder cows (5/14) 35.7%, anestrous heifers (16/26) 61.5% and repeat breeder heifers (5/14) 35.7%. This treatment protocol may improve fertility outcomes in zero-grazed units where anestrus is a problem, reproductive skills are deficient, there is scarcity of labor or where there is an inability to commit the required time for estrus detection. Kenya Veterinarian Vol. 30 (2) 2006: pp. 68-72

Longitudinal observation on reproductive and lactation performances of smallholder crossbred dairy cattle in Fitche, Oromia region, central Ethiopia

A two-year longitudinal study was conducted to assess the reproductive and lactation performances of smallholder crossbred dairy cattle in Fitche, central Ethiopia. Twenty-four smallholder dairy farms were monitored and data on reproductive, breeding, lactation and management aspects of crossbred dairy cows (n=69) were collected and analysed. Moreover, milk samples were collected and analysed for progesterone. The overall Least-squares means for calving interval (CI), calving to conception interval (CCI) and first observed oestrus after calving were 516, 253 and 141 days, respectively. Suckling significantly prolonged these intervals. The mean first onset of luteal activity (OLA) after calving was 52 days, while 67.4% n=43) had a delayed (>55 days) return to cyclicity after calving. Suckling and parity number significantly (p < 0.05) influenced the OLA. The mean lactation length was 54.4 weeks. The overall daily mean milk yield for the first 43 weeks of lactation after calving was 11.7 L/day. The estimated daily milk yield increased slowly and reached peak (13.8 L/day) around the 11th week post partum and declined gradually and steadily. Suckling status, season of calving and parity number significantly influenced the estimated daily milk yield. In conclusion, the present study indicated that the smallholder crossbred dairy cows in the study area had prolonged intervals to first oestrus after calving, to conception and to the next calving, and thus their reproductive performance is unsatisfactory. Delayed first onset of luteal activity (postpartum anoestrus) contributed to these extended intervals. Further detailed investigation is suggested to examine the effects of other relevant factors on the reproductive and lactation performances of smallholder crossbred dairy cows for appropriate intervention.

Control of postpartum anestrous with an intra-vaginal progesterone device plus eCG or calf removal for 120 h in suckled crossbred cows managed in a pasture-based system

To control postpartum anestrus and reduce calving to conception interval, 167 crossbred non-pregnant cows that were 90–130 days postpartum were allotted randomly to one of the following treatments: PH ( n = 59), intra-vaginal sponge with 250 mg of medroxyprogesterone acetate (MAP) for 7 days plus 50 mg of MAP and 5 mg 17-β estradiol (17β-E) in the first day of treatment (day −8), 500 UI eCG (day −3) and 1.5 mg 17β-E in 24 h after sponge removal (day 0); CR ( n = 57), temporary calf removal for 120 h; CG ( n = 51), control group without treatment. Estrus rate differed among treatments ( P < 0.01) being greater in PH (78.2%), followed by CR (52.0%) and CG (22.9%). A greater proportion of cows in the PH (80.0%) and CR (54%) groups had ovulations when compared to CG (35.4%). Intervals to first estrus were 13.5 ± 6.3 days, 26.1 ± 6.4 days and 52.5 ± 7.5 days for the PH, CR and CG groups, respectively. First insemination conception was similar in the three groups. Postpartum intervals to first breeding (PFS) and to conception (PCI) were longer in CG than PH and CR groups ( P < 0.05; P < 0.01). The PH and CR groups had a similar PFS but PCI was different ( P < 0.02). Accumulated pregnancy rate at 30 and 60 but not at 90 days were different (30 days: P < 0.09; P < 0.01; P < 0.09; 60 days: P < 0.06; P < 0.01; P < 0.03) among treatments. After 90 days post-treatment, 9%, 18% and 33% of cows from the PH, CR and CG groups had not conceived. Similarly, 5.4%, 6.0% and 12.5% of cows from the PH, CR and CG groups, respectively, were culled from the herd because of lack of pregnancy after 180 days post treatment. In the group of cows evaluated by ultrasonography, only those cows having larger ovaries and dominant follicles had ovulations. It was concluded that the hormonal treatment was more efficient in inducing a fertile estrus and reducing calving to conception interval followed by the calf removal for 120 h. Each method can be considered as an important tool to reduce the postpartum anestrous period in dual purpose herds when AI is conduct in the tropics.