Nonsuckled Cows Research Articles

Reproductive efficiency in Bos indicus and Bos indicus crossed: impact of timed artificial insemination (TAI) using a progesterone and estradiol benzoate-based protocol

ABSTRACT Data from 15,342 bovine females subjected to timed artificial insemination (TAI) were analysed with the objective of assessing the pregnancy rate (PR) and its association with breed, number of uses of intravaginal implant, body condition score (BCS), animal categories, number of AI, and estrus expression before TAI. The protocol involved administering intravaginal progesterone + estradiol benzoate (day zero), progesterone removal + prostaglandin F2α+estradiol cypionate + equine chorionic gonadotropin (day 8) and TAI + gonadotropin-releasing hormone (day 10) in animals without estrus. Crossbred cows demonstrated higher PR. Non-suckling cows, those with 1st – and 2nd-use implants, and a single-dose implant demonstrated higher PR between categories; the BCS (>2.75–3.5) resulted in better overall PR. There were no differences in the general PR between number of AI. 2nd-use implants resulted in a better overall PR. Primiparous cows resulted better PR with 3rd-use implants. Animals in estrus before TAI demonstrated a higher PR. In conclusion, this study observed no significant differences in general PR among number of AI. Second-use implants were effective. Crossed and non-suckling cows, and 1st – and 2nd-use and single-dose implants exhibited higher fertility. Estrus before TAI favoured PR.

Factors affecting calving to service interval in crossbred Friesian cows in a large dairy farm

To determine the calving to service interval and its associated factors, 125 crossbred Friesian cows were studied. The farm records were randomly examined, and related data were collected on genotype, age, body weight, body condition score (BCS), parity, milk yield, suckling status and season of first postpartum service. The overall calving to service interval in Friesian crossbred cows was 98.9 ± 42.6 days. Calving to service intervals in cows with 50.0%, 62.5 - 68.8% and 75.0 - 87.5% exotic blood were 98.7 ± 41.6, 102.9 ± 58.3 and 94.7 ± 33.6 days, respectively. The calving to service interval in cows aged 42 - 60, 61 - 78 and 79 - 173 months was 74.0 ± 14.4, 108.5 ± 48.9 and 100.8 ± 43.0 days, respectively. The calving to service interval in cows with body weight 140 - 180, 181 - 220 and 221 - 250 Kg was 94.3 ± 38.4, 99.3 ± 41.4 and 134.2 ± 74.9 days, respectively. The calving to service interval in cows with BCS 2.5 - 3.0 and 3.5 - 4.0 was 98.8 ± 42.3 and 99.1 ± 44.3 days, respectively. The calving to service interval in cows with parity 1, 2 - 3 and 4 - 10 was 117.5 ± 76.4, 99.6 ± 40.0 and 96.4 ± 41.2 days, respectively. The calving to service interval in cows with milk yield 0 (dry), 1 - 5, 6 - 10 and 11 - 16 litres was 118.4 ± 51.2, 99.6 ± 45.6, 102.5 ± 45.8 and 84.0 ± 22.1 days, respectively. The calving to service interval in suckling and nonsuckling cows was 100.5 ± 44.3 and 88.8 ± 28.8 days, respectively. The calving to service interval in cows in summer, rainy and winter season was 98.8 ± 41.4, 104.5 ± 46.9 and 95.3 ± 41.9 days, respectively. The difference in calving to service interval among cows of different ages was significant (P<0.05). It is suggested that calving to service interval was not influenced by breed, body weight, BCS, parity, milk yield, suckling status or season of service.
 Bangl. vet. 2021. Vol. 38, No. 1-2, 33–41

Comparison of two intravaginal progesterone-releasing devices in shortened-timed artificial insemination protocols in beef cattle

Commercially available intravaginal progesterone (P4) devices differ in shape, surface area and P4 load, which may affect the resulting pregnancy per AI (P/AI) following timed-AI (TAI). The objective of this study was to compare two intravaginal P4 devices on estrus rate, follicular dynamics and P/AI in beef cattle subjected to shortened-TAI protocols. In Expt. 1, nulliparous heifers were randomly assigned to a P4-releasing intravaginal device (PRID-Delta, 1.55 g P4) or a controlled internal drug release (CIDR, 1.38 g P4) at the initiation of a J-synch protocol. Heifers that displayed estrus 72 h following device removal were TAI, or if not in estrus given GnRH at 72 h and TAI at 90 h. In Expt. 2, nulliparous heifers and non-suckling cows were randomly assigned to either PRID or CIDR groups and either 1 or 2 mg of estradiol benzoate (EB) at initiation of a J-synch protocol. All cattle were TAI concurrent with GnRH 72 h after device removal. In Expt. 3, nulliparous heifers and suckling cows were randomly assigned to either PRID or CIDR groups and initiated a 5-d Cosynch protocol, with TAI concurrent with GnRH 72 h following device removal. In each experiment, cattle received estrus detection patches at device removal, which were then scored from 0 to 3 based on color change between initial application and TAI; 0 = unchanged, 1 = ≤50% change, 2 = >50% change, 3 = missing. Estrus was defined to have occurred when the patch was scored 2 or 3. Transrectal ultrasonography was used to determine cyclicity, diagnose pregnancy in all experiments, and the size of the ovulatory follicle in Expt. 3. In Expt. 1, the estrus rate was greater (72.0% vs. 61.0%; P = 0.04) in the PRID compared to the CIDR group. In Expt. 2, a parity by EB dose interaction (P = 0.02) was attributed to an increased estrus rate (52.8% vs. 41.4%; P = 0.05) in heifers given 1 vs. 2 mg EB. In Expt. 3, there was no difference in the ovulatory follicle diameter at device removal (P = 0.22) or TAI (P = 0.28) between P4 groups. Treatment with a PRID tended (P = 0.10) to increase the P/AI in cows compared to a CIDR (73.5% vs. 61.0%). In all experiments combined, the overall P/AI tended to increase (55.2% vs. 51.0%; P = 0.08) and P/AI in cattle exhibiting estrus increased (64.4% vs. 59.7%; P = 0.02) in cattle given a PRID compared to those given a CIDR, respectively. In summary, the type of intravaginal P4 device affected estrus response and P/AI following TAI in beef cows.

Effect of cow-calf contact on cow motivation to reunite with their calf

Early cow-calf separation prevents much of cows’ natural maternal behaviour. Early separation is thought to prevent the development of a cow-calf bond. To assess this bond, we measured motivation of dairy cows to reunite with their calf. To vary the degree of bonding, some cows were allowed continued contact with their calf and others were separated from their calf soon after birth, following standard practice on most farms. Among cows allowed continued contact, some were able to suckle their calf and others were prevented from suckling (by covering the cow’s udder with an udder net). Cows were habituated to the weighted-gate apparatus before calving by daily training with the (un-weighted) gate. After calving, cow willingness to use the gate was assessed by determining if she would push open the gate to access to her own calf. Testing occurred once daily, with weight on the gate gradually increased. After passing through the gate, the dam’s calf-directed behaviour was recorded. Suckled cows pushed a greater maximum weight (45.8 ± 7.8 kg) than separated cows (21.6 ± 6.7 kg) and non-suckled cows (24.3 ± 4.5 kg), with no differences between separated and non-suckled cows. Once reunited, latency to make nose contact and duration of licking did not differ between treatments. We conclude that motivation for calf contact is greater for cows that are suckled.

Relationship of follicle size and concentrations of estradiol among cows exhibiting or not exhibiting estrus during a fixed-time AI protocol

Cows exhibiting estrus near fixed-time artificial insemination (AI) had greater pregnancy success than cows not showing estrus. The objective of this study was to determine the relationship between follicle size and peak estradiol concentration between cows that did or did not exhibit estrus during a fixed-time AI protocol. Ovulation was synchronized in beef cows by applying the CO-Synch protocol [GnRH (100 μg) on day-9, prostaglandin F2α (PGF2α; 25 mg) on day-2, and a second injection of GnRH 48 h after PGF2α (day 0)] to both suckled (experiment 1) and nonsuckled (experiment 2) cows. Follicle size (day 0) and ovulation (day 2) was determined by ultrasonography. Blood samples were collected every 3 or 4 h beginning at the time of PGF2α injection (0 h). Estrus was detected by visual observation with the aid of estrus-detection patches, and cows that ovulated were classified as exhibited estrus (n = 46) or did not exhibit estrus (n = 63). In both suckled and nonsuckled cows, there was a positive relationship between all cows (P < 0.05) and among those that exhibited estrus (P < 0.05) between follicle size and peak estradiol concentration, but no linear relationship (P > 0.50) between follicle size and peak estradiol concentration was observed among cows not exhibiting estrus. Cows that exhibited estrus had greater (P < 0.01) peak estradiol concentrations than cows that did not exhibit estrus. Suckled cows exhibiting standing estrus had greater (P < 0.001) preovulatory concentrations of estradiol beginning 6 h (replicate 1) or 4 h (replicate 2) after the injection of PGF2α on day-2 compared with cows not exhibiting standing estrus. Nonsuckled cows exhibiting standing estrus had greater (P < 0.001) preovulatory concentrations of estradiol beginning at the injection of PGF2α on day-2 compared with cows not exhibiting standing estrus. Furthermore, cows that exhibited estrus had an increased (P < 0.01) rate in the rise in concentrations of estradiol following the PGF2α to peak estradiol than cows not exhibiting estrus. In summary, follicle diameter had a positive relationship with peak concentrations of estradiol, but only among cows that exhibited standing estrus, and estradiol increased earlier in cows that exhibited estrus compared with cows that did not.

Risk factors for postpartum anestrus in crossbred cows in Bangladesh

Ultrasonography and a structured questionnaire were used in a cross-sectional study to gather data on the prevalence and risk factors for anestrus in crossbred cows at =>60 days postpartum in 273 smallholder farms. The prevalence of anestrus was 18%. The odds ratio (OR) for true anestrus was 17.52 and 2.81 times higher (P < 0.05) in cows with poor (=3.5) body condition score (BCS), respectively, compared to those with optimal BCS (2.5-3.5), 2.82 times higher in suckled than in nonsuckled cows (P = 0.03), and 2.53 times higher in cows that calved during the cold season than in those that calved during the hot season (P = 0.03). The OR for anestrus was 1.62 times higher (P = 0.017) in cows managed by an employee than in those managed by the farmers themselves (P = 0.001), and 2.66 times higher (P = 0.003) in small farms (=11 cows). The OR was 0.71 to 0.46 times lower in farms having a guaranteed market to sell milk than those with an uncertain traditional milk market (P < 0.05). Maintaining optimal BCS of cows, farmers' training on management of cattle reproduction, and development of a market linkage to sell milk would improve the number of cows for breeding by 60 days postpartum.

Suckling, weaning, and the development of oral behaviours in dairy calves

Dairy calves are generally separated from their dam at birth. They express non-nutritive oral activities such as licking or sucking other calves or objects, nibbling, or tongue-playing, which have been related to the absence of sucking a teat and ingestive chewing. We hypothesized that the dam, by its presence, can help focus the oral behaviour of calves towards nutritive activities and thereby limit the development of non-nutritive oral activities. To test this hypothesis, we compared calves suckled by their dam against calves separated from their dam at birth and fed milk through a teat (automatic milk feeder). Cow and calf behaviour was observed before weaning and after weaning at 10wk of age.Before weaning, the suckled calves were less active than the artificially fed calves. After weaning, suckled calves tended to spend less time on non-nutritive oral activities than non-suckled calves. Before weaning, suckling cows and non-suckling cows showed similar behaviour. Both cows and calves reacted to weaning: cows showed vocalization and agitation, and calves showed increased blood cortisol levels.We conclude that keeping dairy calves with their dam for 10wk can be beneficial to calves, although weaning induces a degree of stress.

Análise marginal dos custos da utilização de sêmen sexado macho para produção de touros Nelore

The aim of this research was to evaluate the economic viability of using male-sexed semen to Nellore bulls production. The experiment was conducted on two farms of breeders and selectors of Nellore bulls for sale. The females included 433 heifers (2 years old) and 230 non-suckling cows, totaling 663 animals. Average body condition score was 3.25±0.5 (1-5 scale). The total pregnancy rate of females inseminated with male-sexed semen of bulls A, B and C was 38.76% (131/338) lower (p<0.0001) than the total pregnancy rate observed for females inseminated with conven-tional semen from the same bulls (57.85% [188/325]). The use of male sexed semen showed a profit of US$ 1163.43, when compared with conventional semen to Nellore bulls production. It was concluded that the use of male sexed semen is economically viable for Nellore bulls production, but presents greater risks than the use of conventional semen for this purpose.

Pregnancy rate of Nelore females inseminated with male-sexed semen

Pregnancy rates of Nelore females inseminated with male-sexed semen and conventional semen from the same bulls were evaluated. The females included 433 heifers (2 years old) and 230 non-suckling cows, totaling 663 animals. Average body condition score was 3.5 (1–5 scale). Estrus was induced with prostaglandin F2α. The total pregnancy rate of females inseminated with male-sexed semen of bulls A, B and C was 38.8% (131/338) less ( P < 0.0001) than the total pregnancy rate observed for females inseminated with conventional semen from the same bulls (57.9% [188/325]). Pregnancy rates of non-suckling cows inseminated with male-sexed semen was 43.3% (49/113), which was similar ( P ≥ 0.05) to the values found for heifers inseminated with male-sexed semen from the same bulls (36.4% [82/225]). The pregnancy rate of females inseminated with male-sexed semen was less compared with females inseminated with conventional semen. In addition, there was no significant difference in the pregnancy rate of heifers versus non-suckling cows.

Plasma Cortisol Concentrations after CIDR Insertion in Beef Cows

The objective of this study was to show plasma cortisol concentration after treatment with controlled internal drug release (CIDR) in non-suckling beef cows. On day 9 after oestrus, two cows were inserted with CIDR into the vagina for 24 h and the other two cows were treated as a control group. Four days later, the two control cows were treated with CIDR and the other two CIDR-treated cows were used as controls. Cortisol concentrations were determined by ELISA in plasma samples collected before, during and after insertion of CIDR. There was a significant increase in plasma cortisol concentrations (p<0.01) after insertion of CIDR. Mean (± SEM) plasma cortisol concentrations increased from 1.3 ± 0.4 to a peak of 8.8 ± 1.1 ng/ml at 5 h and then decreased to basal concentrations at 7 h after insertion of the device. In conclusion, the insertion of intra-vaginal device causes an increase in plasma cortisol concentrations in beef cows, although the pathophysiological significance of the elevation of cortisol is not known.

178 USE OF A NEW INTRAVAGINAL DEVICE TO RELEASE PROGESTERONE IN FIXED-TIME EMBRYO TRANSFER EMBRYO RECIPIENTS

Progestagen-releasing devices are commonly used for fixed-time artificial insemination and fixed-time embryo transfer (FTET). The aim of this study was to evaluate the efficacy of a new progesterone-releasing intravaginal device made of poly(3-hydroxy)butyrate-valerate copolymer (PHB-V) and poly-ϵ-caprolactone (PCL; Progestar®, Innovare, São Paulo, Brazil) to synchronize crossbredcows and heifers for FTET by determining ovulation, conception, and pregnancy rates. A total of 205 recipients ranging in age from 2 to 8 years (heifers, n = 77; non-suckled cows, n = 69; suckled cows, n = 59) were used on 3 different farms during February, March, and April 2008. The experimental design was a generalized block design (cyclicity, body condition score, postpartum interval, and animal category, i.e. heifers, suckled, or non-suckled cows), with 2 different synchronization treatments for FTET (Progestar® v. Crestar®). Cows were assigned to either Crestar® (norgestomet ear implants; Intervet Schering-Plough, Kenilworth, NJ, USA; n = 103) or Progestar® (PHB-V; n = 102) treatments. All groups were treated with 2 mg of estradiol benzoate i.m. (Innovare) and received the intravaginal or auricular device according to their group (Day 0). Together with P4 device withdrawal (Day 8), all animals received 400 IU of eCG i.m. (Novormon®, Schering-Plough) and 500 μg i.m. of PGF2α, (Sincrocio®, Ouro Fino, Brasil). On Day 9, all cows were treated with 1 mg of estradiol benzoate (Innovare) and the innovulation was performed on Day 17. Embryos were maintained at 37°C during the innovulation period. The percentage of usable recipients (AR) based on the presence of a functional CL on the day of embryo transfer, conception rate (numbers of pregnant recipients of the total number transferred; CR), and pregnancy rate (numbers of pregnant recipients of the total number synchronized; PR) were determined by ultrasonography 23 days after embryo transfer. Data were submitted to ANOVA (PROC GLM, SAS Institute Inc., Cary, NC, USA) and significant differences were considered to have a P-value of &lt;0.05. None of the interactions were significant and there was no effect of treatment on AR (72.8% v. 83.3%), CR (47.9% v. 42.7%), and PR (34.7% v. 35.0%) for Progestar® v. Crestar® groups, respectively. This experiment showed that Progestar® was as efficacious as Crestar® to synchronize crossbred cows and heifers for FTET. FAPESP-Fundação de Amparo à Pesquisa do Estado de São Paulo and CNPq-Conselho Nacional de Desenvolvimento Científico e Tecnológico.

Effect of indoor energy restriction level and management on beef production in Belgian Blue double-muscled cow-calf pairs

One hundred and twenty-six cows were involved to investigate the impact of energy (E) restriction (100%, 90%, 80% and 70% of total energy requirements) during the indoor period and two calf management systems (CMS: suckling or rearing). An E restriction during the indoor period resulted in a loss of body weight, even for E100, which was compensated during the re-alimentation period, but body weight remained lower in suckling than in non-suckling cows. The cows yielded 213 full-term gestations and 8 abortions. Abortion was not affected by E (p = 0.187) or CMS (p = 0.804). Calving interval was neither affected by E (p = 0.775) but tended to be longer in suckled cows (p = 0.087). E reduced body weight and body condition score (BCS) at the end of the calving interval, while CMS only affected BCS. E70 resulted in a higher colostrum yield than E100 and E 90 but immunoglobulin content was not affected (p = 0.759). Cow culling was not affected by E or CMS. It increased from 12.9% to 22.2% and 32.5% for cows with a BCS at parturition lower than 1.5 or between 1.5 and 2.0, or higher than 2 respectively. Calf birth weight was neither affected by E or CMS, but there was an interaction between E and dam age (p = 0.050). Increasing the E restriction tended to reduce calf survival (p = 0.089). Performance of the surviving calves was not affected by E, but suckling calves gained faster than rearing calves (p < 0.001). Beef production by the cow-calf pair was not different between energy levels (p = 0.738), but it was 10.8% lower for E70 than for E100 cows. It is not appropriate to apply an E restriction of more than 10-20% for maximum cow reproductive traits and calf performance.

Effect of Suckling on the Reproductive Performance and Metabolic Status of Obese Japanese Black Cattle during the Early Postpartum Period

The aim of our study was to investigate the effects of suckling on reproductive performance and metabolic status of obese (mean body condition score of more than 4.0 on a scale of 1-5) maternal Japanese Black cows during early postpartum period. We used 7 postpartum Japanese Black cattle. Four cows were suckled ad libitum (suckled) until completion of their first artificial insemination (AI), while 3 cows were not suckled at all because they were separated from their calves immediately after parturition (non-suckled). Body weight and plasma concentrations of metabolites and hormones were measured from wk 1 to 9 postpartum. Ovarian activity was detected using plasma progesterone concentration, and all cows received their first AI after application of the Ovsynch protocol at approximately 4 months postpartum. Although body weights of non-suckled cows increased during experimental period (P<0.05), those of suckled cows remained unchanged. Plasma concentrations of glucose of non-suckled cows were higher at wk 2 postpartum (P<0.05) and their levels of non-esterified fatty acid tended to be lower at wk 1 and 2 postpartum compared with suckled cows (P<0.1); however, these differences between groups were not observed with progression of postpartum period. In addition, plasma insulin concentrations of non-suckled cows were higher than those of suckled cows during experimental period (P<0.05). During sampling period (wk 0 to 9 postpartum), onset of normal ovarian cycle was observed in all non-suckled and 2 of 4 suckled cows, and it was delayed in other 2 suckled cows compared with non-suckled cows; however, 3 suckled cows conceived at the first AI after application of the Ovsynch protocol; none of non-suckled cows conceived at this time. Overall, we suggest that suckling seems to reduce increase of body weight after parturition, although it does not improve obesity, and influences conception despite delay in resumption of normal ovarian cyclicity in obese Japanese Black cows.

Uso do protocolo Crestar® em tratamentos utilizando benzoato de estradiol, PGF2±, PMSG e GnRH para controle do ciclo estral e ovulação em vacas de corte

O objetivo foi avaliar a eficiência do controle da ovulação utilizando os hormônios PMSG, GnRH, Benzoato de Estradiol e PGF2a junto ao protocolo CrestarÒ, para IA em tempo fixo. Foram utilizadas 348 vacas, cruzadas Nelore (Bos taurus indicus) X Charolês (Bos taurus taurus), divididas em dois grupos: 179 vacas paridas com 90 a 120 dias pós-parto e 169 vacas solteiras. Estes animais foram submetidos a cinco tratamentos: todas as vacas receberam o protocolo Crestar® como agente sincronizador do crescimento folicular. (implante subcutâneo com 3mg de norgestomet e injeção 3mg de norgestomet + 5mg de valerato de estradiol - i.m.). Após a remoção do implante (10 dias), as vacas foram submetidas aos cinco tratamentos de controle da ovulação: T1 - (n=70): injeção de solução fisiológica 48h após a retirada do implante (D 12); T2 - (n=68): 0,75mg de benzoato de estradiol 24h após a retirada do implante (D 11); T3 - (n=70): aplicação de 150mg de PGF2a, no dia da retirada (D 10) e 0,75mg de benzoato de estradiol 24h após a retirada do implante (D 11); T4 - (n=70): 500 UI de PMSG na retirada do implante (D 10) e T5 - (n=70): 500mg de GnRH 48h após a retirada dos implante (D 12). Todos os animais foram inseminados 54-56h após a retirada do implante. As taxas de prenhez foram analisadas estatisticamente por regressão logística. Não houve diferença entre os tratamentos (p&gt;;0,05) onde: 35,7, 31,4, 22,0, 37,0 e 42,8% para T1, T2, T3, T4 e T5 respectivamente.

Reproductive Disorders of Crossbred Dairy Cows in the Central Highlands of Ethiopia and Their Effect on Reproductive Performance

The study was conducted to estimate the proportion of reproductive disorders and to determine factors affecting reproductive performance of crossbred dairy cows under four different production systems in the central highlands of Ethiopia. The principal postpartum reproductive disorders were retained fetal membranes (14.7%) and uterine infection (15.5%). Anoestrus was the major postpartum reproductive problem in the mixed crop-livestock production system (38.6%) and was significantly associated with this production system. Apart from anoestrus, the occurrence of reproductive disorders was not significantly associated with a production system. Most of the reproductive disorders occurred as a complex rather than as a single abnormality. Two or more abnormal conditions were seen in 11.4% of the cases. Each reproductive trait measured was affected adversely by reproductive disorders. Cows with reproductive disorders in each production system, lactation group and suckling and non-suckling group had longer intervals from calving to first service and to conception (p < 0.001) and required more services per conception (p < 0.001). Pregnancy rate and conception to first service were 84.7% and 51.7%, respectively, for cows without reproductive health problems; and 64.2%, and 15.1%, respectively, for cows with reproductive disorders (p < 0.001). Overall, intervals from calving to first service were shorter (p < 0.05) than in younger cows. Intervals from calving to first service and to conception were longer in suckling than in non-suckling cows (p > 0.05). Cows with a good body condition score (> 3.5) at calving had shorter calving to first service and conception intervals than cows in poor condition (p < 0.001). The results showed that reproductive abnormalities, coupled with poor body condition, are important factors that contributed to reproductive inefficiency. An appropriate reproductive health management, a reliable artificial insemination service and supplementary feeding could be the management options to reduce or alleviate some of the problems.

Response of beef heifers and non-suckling beef cows to different oestrous synchronization protocols

AbstractThe objective was to evaluate different oestrous synchronization schemes in beef cattle under range conditions. In experiment 1, 202 heifers averaging 26 months of age were assigned randomly to three treatments: (a) GnRH-PG. (no. = 44) day 0 (D0): injection of GnRH; D7: injection of PGF2α; D0 to D25 oestrous detection (OD) and artificial insemination (AI); (b) OD-PG. (no. = 45) D0 to D4; OD + AI; D5: injection of PGF2α; D5 to D25 OD + AI; and (c)Ovsynch. (no. = 113) D0: injection of GnRH; D7: injection of PGF2α; D9: injection of GnRH and 16 h later AI at fixed time. In experiment 2, 318 non-suckling cows were assigned randomly to three treatments: (a) GnRH-PG. (no. = 106) D0: injection of GnRH; D7: injection of PGF2α; D0 to D25 OD + AI; (b) GnRH-MAP-PG. (no. = 106) D0: injection of a GnRH analogue and insertion of an intravaginal sponge impregnated with 250 mg of medroxyprogesterone acetate; D7: injection of PGF2α and sponge withdrawal; D0 to D25 OD + AI; (c) controls. (no. = 106) OD and AI. The experimental period lasted 25 days and, with exception of the Ovsynch treatment, oestrous detection was carried out twice a day (a.m./p.m.) and inseminations performed 12 h later. The pregnancy rates assessed by ultrasonography 30 days after AI were: experiment 1: (a) 30·0%; (b) 28·6% and (c) 62·3% (P &lt; 0·05); experiment 2: (a) 60·2%; (b) 57·8% and (c) 45·5% (P &lt; 0·05). It is concluded that in heifers and non-suckling cows, oestrous synchronization treatments result in higher pregnancy rates. In non-suckling cows, the addition of a progestagen did not improve the response.

Follicular dynamics during postpartum anestrus and the first estrous cycle in suckled or non-suckled Brahman ( Bos indicus) cows

Brahman ( Bos indicus) cows, were selected at 28±10 days after calving and analyzed by real time rectal ultrasonography three times a week, in order to evaluate and compare follicular and corpus luteum development during postpartum (PP) anestrus and the first PP estrous cycle under sylvopastoril conditions. Suckling (S, n=11) or non-suckling (NS, n=5) cows were evaluated in a zone of tropical dry forest (450 m of altitude, mean temperature=27°C, annual rainfall=1000 mm). Estrous detection was performed twice daily by direct observation. Progesterone was quantified using RIA. From 28±10 days postcalving to resumption of estrous cycles, there were no differences ( P>0.05) between NS and S cows for diameter of the dominant or first subordinate follicle, follicular growth rate, or interdominance interval. Silent ovulation, corpus luteum formation and subsequent progesterone concentrations ranging from 0.3 to 9.7 ng/ml, were found in both groups. The first calving to ovulation and calving to standing estrus intervals were shorter ( P<0.01) in NS (34.8±5.81 and 41.2±9.03 days) than in S (65±4.82 and 81±6.21 days) cows. Follicular development and progesterone concentrations during the first PP estrous cycle did not differ ( P>0.05) between NS and S cows. These results suggest that Brahman cows could have an early PP resumption of follicular recruitment if fed under sylvopastoril system conditions. However, non-suckled cows did have an earlier standing estrus and ovulation than did suckled cows.

The effect of restricted suckling and non-suckling systems on dairy cow and calf behaviour

Artificial rearing necessitates stressful cow-calf separation (Lefcourt and Elsasser, 1995; Hopster et al, 1995) and precipitates cross-suckling (Lidfors, 1993). Thus, suckling systems may improve the welfare of cows and calves, by alleviating 'stressful' cows-calf separation and satiating suckling motivation. The aim of this experiment was to compare behaviour in cows and calves in restricted suckling and non-suckling systems.Thirty six multiparous dairy cows and calves were divided at 4 days postpartum into three groups. The treatment groups were; non-suckled (NS) cows with calves artificially reared (AR), cows suckled by their own calf (RSM) and cows suckled by a foster calf (RSF). Suckling took place for 15 minutes following mechanical milking only.

The effect of restricted suckling and non-suckling systems on dairy cow and calf behaviour

Artificial rearing necessitates stressful cow-calf separation (Lefcourt and Elsasser, 1995; Hopster et al, 1995) and precipitates cross-suckling (Lidfors, 1993). Thus, suckling systems may improve the welfare of cows and calves, by alleviating 'stressful' cows-calf separation and satiating suckling motivation. The aim of this experiment was to compare behaviour in cows and calves in restricted suckling and non-suckling systems.Thirty six multiparous dairy cows and calves were divided at 4 days postpartum into three groups. The treatment groups were; non-suckled (NS) cows with calves artificially reared (AR), cows suckled by their own calf (RSM) and cows suckled by a foster calf (RSF). Suckling took place for 15 minutes following mechanical milking only.

Influence of suckling on calving interval of N'Dama cows in The Gambia.

The inhibitory influence of the suckling stimulus on resumption of cyclicity post partum was elucidated for dairy cows by Oxenreider (1968) and for beef cattle by Short et al. (1972). In the traditionally managed herds in West Africa calves suckle their dam initially to stimulate milk let down, the cows are then milked and the calf is allowed to suckle the residual milk. Under such management calves normally suckle their dams for the entire lactation (mean 420 days, s.d. 138.6) as reported by Agyemang et al. (1990). In a trial to study milk conversion in the calf described by Agyemang et al. (1993) cows were allocated at calving to either a group in which they were milked the traditional way (n = 20), or to a group where calves were not allowed to suckle except for the first 4 days (n = 16). In the latter group milk let down was stimulated by oxytocin injection before morning and evening milking. All the cows were managed in the same herd and calved within a range of 2 months to avoid bias due to seasonal or nutritional influences. A fertile bull was always present in the herd. This study continues the work by Agyemang et al. (1993) by analysing the subsequent calving records of the dams to determine the differences in calving interval (CI) between the groups of suckled and non suckled cows. A summary of the data is given in Table I and these were analysed using the Wilcoxon 2 sample test. It was found that 60% of the non suckled cows had a CI of less than 390 days while 60% of the suckled cows had not calved by 480 days postpartum. The difference in the mean between the 2 groups of 138 days in favour of the non suckled group is highly significant (P < 0.01). The fate of 6 animals (37.5%) of the non-suckled group was not known and could not be determined in retrospect. Since these could have been cows with a very high CI a comparison was also made between the mean CI of the non-suckled group and 62-5% of the best animals of the suckled group revealing a reduced mean CI of 50 days in favour of non-suckled cows, 456 days and 406 days respectively.