Individual Heifers Research Articles

16 MODIFICATION TO INTRAVAGINAL PROGESTERONE + ESTRADIOL-BASED ESTROUS SYNCHRONIZATION PROTOCOLS TO IMPROVE OVARIAN RESPONSES IN BOS INDICUS HEIFERS

Estrous synchronization (ES) protocols for fixed-time AI (FTAI) have been mainly developed for Bos taurus cattle assuming that usage in Bos indicus cattle results in similar outcomes. Unexplained variation in the reproductive outcomes of these treatments in extensively managed Bos indicus herds has limited the adoption of FTAI. The aim was to evaluate the ovarian function in heifers treated with different doses of progesterone (P4). Brahman (n = 30) and Brahman-cross (n = 34; 3/4 to 7/8 Brahman) heifers weighing an average of 285 kg (248 to 323 kg) and 307 kg (250 to 363 kg), respectively, were allocated at random to 1 of 4 treatment groups: 1) full-dose Cue-Mate (CM100; two P4-impregnated pods, 1.56 g of P4; Bioniche Animal Health Aust/Asia, Armidale, NSW, Australia; n = 17); 2) half-dose Cue-Mate (CM50; one P4-impregnated pod; 0.78 g of P4; n = 15); 3) half-dose Cue-Mate + 300IU of eCG (CM50+G; Pregnecol, Bioniche Animal Health, Aust/Asia; n = 14) i.m. at Cue-Mate removal; and 4) double PGF2α group (PG; n = 18). Heifers in the P4-treated groups received 1 mg of EB (estradiol benzoate; Ciderol; 1 mg mL-1; Genetics Australia, Bacchus Marsh, Victoria) at Cue-Mate insertion (Day -10) and 24 h after Cue-Mate removal (Day -1) and 250 μg of PGF2α (Cloprostenol, Estromil, Ilium Veterinary Products, Smithfield, Australia) i.m. at Cue-Mate insertion (Day -10) and removal (Day -2). Heifers in the PG group received 500 μg of PGF2α on Day -16 and Day -2 i.m. Ovarian function was evaluated twice daily by transrectal ultrasonography on Day -1, Day 0 (expected estrus), and Day 1, and once daily on Days 4, 6, 8, 10, 12, and 16 of the synchronized and return cycles. Concurrent blood samples were collected to determine plasma P4 concentrations. A one-way ANOVA was used to analyze follicle diameter variables and Fisher’s Exact test was used to analyze all other data reported (StataCorp 2007, College Station, TX, USA). There was no difference (P = 0.31) in the diameter of the dominant follicle 54 to 56 h post-Cue-Mate removal (the time FTAI would be conducted) in the CM100 (11.5 ± 1.1), CM50 (13.3 ± 1.5), CM50+G (13.7 ± 1.5), or PG (14.5 ± 0.7) groups. Synchrony of ovulation in ovulating heifers did not differ (P < 0.05) between the P4-treated groups with 12/13 (CM100), 11/12 (CM50), and 9/12 (CM50+G) heifers ovulating within 53 to 77 h after Cue-Mate removal, but was lower (P < 0.02) for the PG group (1/5). Individual heifer P4 profiles revealed that 2/15, 1/15, 3/12, and 0/5 of heifers that ovulated in the CM100, CM50, CM50+G, andPG groups, respectively, failed to re-ovulate in the return cycle. Also, 1/15, 3/15, 1/12, and 0/5 of heifers that ovulated in the CM100, CM50, CM50+G, and PG groups, respectively, developed a CL that persisted into the return cycle. This study shows the potential benefits of using intravaginal devices containing a lower amount of P4 to induce synchronized ovulation in Brahman heifers, consistent with the findings of Carvalho et al. (2008 Theriogenology 69, 167).

Trainability of eliminative behaviour in dairy heifers using a secondary reinforcer

Soiled bedding influences cleanliness and disease levels in dairy cows and there is no evidence of an inherent latrine behaviour in cattle. If cows were trained to use a concrete area of the housing system as a latrine, a cleaner bed could be maintained. Thirteen group-housed, 14–16-month-old Holstein-Friesian heifers, were clicker trained with heifer-rearing concentrate pellets as a reward. Training was carried out in four phases. (Phase 1) Association of feed reward with clicker, criterion: 34/40 correct responses. (Phase 2) Simple task (nose-butting a disc) to reinforce phase 1 association, criterion: 17/20 correct responses. (Phase 3) Association of eliminative behaviour with reward where criterion was four sessions with only one incorrect response: criteria for each heifer in phases 1–3 were set using binomial tests. (Phase 4) Shaping eliminative behaviour to occur on concrete. Possible responses were, eliminating on concrete (C) or straw (S), or moving from one substrate to another immediately before eliminating: C → S, S → C. Heifers were rewarded for the desired behaviours C and S → C and ignored when S and C → S occurred. If learning was achieved, C should increase as C → S decreased and S → C should increase as S decreased: tested with Spearman rank correlations. All heifers achieved criterion by day 4 of phase 1 ( P = 0.001); day 1 of phase 2 ( P = 0.001) and day 10 of phase 3 ( P < 0.009). Responses changed throughout phase 3 beginning with (i) looking at the trainer whilst voiding then moving to trainer after the click, and later including (ii) moving to trainer immediately before- or (iii) during voiding. No relationship was found between S and S → C ( r s = −0.14; P = 0.63) or C and C → S ( r s = −0.33; P = 0.25). All group members eliminated more often on concrete (580) than on straw (141) but four heifers with consistently longer lying bouts also showed more C → S before lying down (Mann–Whitney, P = 0.007). The present study is believed to be the first reported work to show that cattle can be trained to show an awareness of their own eliminative behaviour. This was not successfully shaped to latrine behaviour, however, and it is suggested that floor type may not have been a sufficiently salient cue. Voiding on straw occurred largely with response C → S (0.73) and general behaviour suggested that this was strongly linked to lying patterns of individual heifers.

The influence of iodine teat dipping and an external teat sealant in heifers on bacterial isolation from quarter milk culture obtained post-calving

A longitudinal observational 2 year field study including 178 dairy herds was conducted in Norway. The aim of the study was to investigate the influence of iodine post milking teat dipping (PMTD) and an external teat sealant (ETS) in first calvers (heifers) on bacterial isolation from milk culture post-calving. Every heifer was either sampled in connection with a clinical mastitis (CM) event at calving or otherwise approximately 6 days post-calving. Milk culture results were available from 3218 individual heifers and 12,872 quarter milk samples. Separate multivariable logistic regression models were used for each bacterium. Neither use of PMTD nor ETS did decrease the risk of bacterial isolation post-calving. However, if iodine PMTD had been used, there was an increased risk of clinical mastitis (Odd ratio (OR) = 1.6 (0.9–2.7)) and an increased risk of isolation of coagulase negative staphylococci OR = 1.5 (1.0–2.1). If ETS had been used, there was an increased risk of isolation of coliform bacteria (coliform and Escherichia coli) (OR = 2.9 (1.2–7.3)). There was significantly less Streptococcus dysgalactiae during the summer and autumn compared to the winter and spring. There was a significant herd effect for Streptococcus uberis and for coliforms with an OR = 5.1 (2.1–12) and 4.5 (2.7–7.6) respectively.

Effect of organic or inorganic trace mineral supplementation on follicular response, ovulation, and embryo production in superovulated Angus heifers

We determined whether source of trace mineral supplementation prior to embryo collection affected embryo production and quality. Angus half-sibling heifers ( n = 20) originating from a common herd were assigned to three treatment groups using a 3 × 3 latin square design replicated in time (3×) and space (6× complete and 1× incomplete): (1) heifers received no added mineral to their diet (control; n = 53); (2) heifers received a commercially available organic mineral supplement (organic; n = 52); or (3) heifers received an all inorganic mineral supplement (inorganic; n = 55). All heifers had ad libitum access to hay and were fed a supplement containing corn and soybean meal. Treatments were initiated 23 days prior to embryo recovery. Heifers were given a 45-day adaptation period of no mineral supplementation before initiating a new treatment. Ovarian structures were evaluated using transrectal ultrasonography to determine the presence and number of follicles and CL on each ovary. The mean number of recovered ova/embryos was similar among treatments (4.1 ± 0.7, 3.8 ± 0.7, and 3.3 ± 0.7 for control, inorganic, and organic treatments, respectively), the number of unfertilized oocytes was greater ( P < 0.05) for inorganic (2.3 ± 0.5) and control (1.6 ± 0.5) treated heifers than organic (0.4 ± 0.4) treated heifers. No differences among treatments existed for the number of degenerate or transferable embryos, but individual heifer influenced the total number of embryos/ova, unfertilized ova, and transferable embryos recovered. We conclude that heifer accounted for the greatest differences in embryo production and quality. Source of trace mineral supplementation did not significantly alter embryo number or quality in superovulated purebred Angus heifers fed a well-balanced diet, meeting all trace mineral requirements.

Effect of individual heifer oocyte donors on cloned embryo development in vitro

The aim of this study was to determine the effect of individual oocyte donors on cloned embryo development in vitro. Five Holstein heifers of varied genetic origins were subject to ovum pick up (OPU) once weekly. In total, 913 oocytes were recovered from 1304 follicles. A mean of 7.7 ± 0.4 oocytes was recovered per session per animal. Individual mean oocyte production varied significantly in quantity but not in quality (morphological categories) among heifers. Oocytes from individual heifers were used as recipient cytoplasm for somatic cell nuclear transfer (SCNT). Cumulus cells, collected from a single Holstein cow genetically unrelated to the oocyte donor, were used as donor cells. Although the percentage of reconstructed embryos that started to cleave was nearly constant, the percentage of cleaved embryos that developed into blastocysts showed clear individual heifer variation (61%, 51%, 31%, 28% and 24%, respectively), with a mean of 38% showing blastocyst formation. In vitro fertilization (IVF) was also conducted with oocyte from the same heifers used in SCNT. A variation of blastocyst production among individual heifers was also shown in the IVF experiment, but the rank of oocyte donor based on the blastocyst rate was changed. In conclusion, individual oocyte donor may have an effect on cloned embryo development in vitro, which differed from the effect on IVF embryos.

Effects of stocking rate on methane and carbon dioxide emissions from grazing cattle

Pastoral farming contributes significantly to total agricultural emissions of greenhouse gases, and stocking rate is the simplest grassland management decision. A study was conducted during the 2002 and 2003 grazing seasons on a semi-natural grassland in the French Massif Central in order to measure enteric methane (CH 4) and total carbon dioxide (CO 2) emissions from Holstein-Friesian heifers (initial liveweight (LW) 455 ± 29 and 451 ± 28 kg in 2002 and 2003, respectively) managed at low (LSR) and high (HSR) stocking rates (1.1 LU ha −1 versus 2.2 LU ha −1, respectively) under a continuous grazing system. Measurements took place in late spring, mid summer, late summer and early autumn. Daily CH 4 and CO 2 emissions by individual heifers were measured during 7 consecutive days in each period using the sulphur hexafluoride (SF 6) tracer technique. In both grazing seasons, the herbage in the LSR system had higher mass (HM) than in the HSR system, especially in mid and late summer. In both grazing seasons, herbages offered in the LSR system were of lower quality than those in the HSR system, and consequently feed organic matter (OM) digestibilities (OMD) and intakes (OMI) in the LSR system were lower ( P < 0.01) than in the HSR system. In both grazing seasons, heifer LW increased as the seasons progressed ( P < 0.001), and heifers in the HSR system tended to be heavier than those in the LSR system. Systems did not differ ( P > 0.05) in mean absolute CH 4 emission (223 g d −1 versus 242 g d −1 and 203 g d −1 versus 200 g d −1 for LSR and HSR in the 2002 and 2003 seasons, respectively), but as the seasons progressed, CH 4 emission per unit of digestible feed intake was higher ( P < 0.05) in the LSR than in the HSR treatment. Both absolute CH 4 emission (g d −1) and CH 4 yield (CH 4 energy loss as a percentage of gross energy intake, % of GEI) were consistently related ( P < 0.05) to OM intake (both gross and digestible). The SF 6 tracer technique appeared to overestimate total CO 2 emission from heifers. Nevertheless, significant ( P < 0.01) coefficients of correlation were found between measured CO 2 emissions and LW ( r = 0.68 and 0.41 in season 2002 and 2003, respectively), and these correlations were stronger for HSR-managed heifers than LSR-managed heifers. This study found no effect of SR system on enteric CH 4 emissions from heifers. The study also found that the SF 6 tracer technique seemed to overestimate CO 2 emission.

81 COMPARISON OF DEVELOPMENTAL ABILITY AMONG CLONED EMBRYOS WITH VARIOUS INDIVIDUAL RECIPIENT CYTOPLASMS IN BOVINE

Faithful reprogramming ensures the proper activation of genes during embryonic development of the somatic cell nuclear transfer (NT) in bovine. It is unambiguous that all these remodeling factors are presented in the oocyte cytoplasm (Du et al. 2002 Mol. Reprod. Dev. 63, 183–191). It will be interesting to determine if the recipient cytoplasms derived from individuals have different development ability and reprogramming competence during NT. Oocytes recovered by Ovum pickup from five Holstein heifers at 14 months of age were used as recipient cytoplasms. Cultured granulosa cells of the same origin were used as donor cells. Oocytes were enucleated at 20 h post-maturation and a single donor cell was transferred into the perivitelline space of a recipient oocyte. After fusion and activation, the reconstructed embryos were cultured in B2 medium (Laboratoire CCD, Paris, France) on a monolayer of Vero cells for 7 days. The oocyte number, development ability, and NT efficiency of recipient cytoplasm derived from each individual were compared (Table 1). Differences among individuals were verified using a chi-square test, SAS 6.12 version (SAS Institute, Cary, NC, USA). There were significant differences of survival after fusion and the rate of development to the blastocyst stage for embryos reconstructed with recipient cytoplasm from five different individual heifers (P &lt; 0.05). However, maturation rate, fusion rate and cleavage rate of embryos reconstructed with recipient cytoplasm from five different individual heifers presented no significant differences (P &gt; 0.05). Reconstructed embryos with recipient cytoplasm from one heifer (03025) showed a lower survival after fusion (61% vs. 80%, 86%, 77%, 91%) but a higher ability to develop to blastocyst stage (61% vs. 24%, 31%, 52%, 31%) than the embryos from the other four heifers. The current study showed that recipient cytoplasm from various individuals may present great differences in developmental ability in nuclear transfer. This may result from different compatibility between nucleus and mitochondria or the content of maternal RNA as well as proteins in the oocyte. Further studies are needed to elucidate the genetic factors that affect the reprogramming in nuclear transfer. Table 1. Nuclear transfer efficiency with various individual recipient cytoplasms

Variation in the load of the horn fly, Haematobia irritans, in cattle herds is determined by the presence or absence of individual heifers.

The distribution of horn flies, Haematobia irritans (L.) (Diptera: Muscidae), in herds of Danish Holstein-Friesian cattle was investigated in two studies conducted during two field seasons. In the first study, highly significant differences in fly distribution between the most and the least fly-susceptible heifers were observed. In one herd, the mean difference between the most fly-susceptible and the most fly-resistant heifers was 268 Ha. irritans specimens. The highest ratio between upper and lower mean fly number was 64.1:1, whereas the lowest was 3.1:1. In the second year, it was demonstrated that the heifers kept their rank in fly attraction over time. The trial clearly demonstrated that some heifers were attracting flies, whereas others, even in the same herd, only carried a few. In the second study, heifers were moved in and out of herds in an attempt to manipulate fly loads in the herds. In year 1, one herd (herd A) received four fly-resistant heifers from another herd (herd B), resulting in a drop in the mean number of flies, whereas herd B received four fly-susceptible heifers from herd A, resulting in an elevation of the mean number of flies. In year 2, a similar pattern emerged using herds C and D, and when the cattle were later returned to their original herds, the fly loads returned to their original distribution. The data presented here show unequivocally that, for horn flies, there can be considerable differences in fly loads for individual heifers within the Holstein-Friesian breed. Furthermore, the overall fly load within herds can be manipulated, and can be reversed. Thus, the distribution in the number of flies within a herd appears to depend on the number of fly-resistant or fly-susceptible heifers. The possible role of chemical factors emitted by heifers, i.e. volatile semiochemicals, in determining differences in fly loads is discussed, whereby attractants are emitted by fly-susceptible heifers and enable flies to locate their host, and repellents are emitted by fly-resistant heifers such that the flies are actively repelled from the herd.

Effects of Supplement Type on Growth and Pregnancy Rate of Yearling Brahman-Crossbred Heifers

The effects of winter supplement type on growth and pregnancy rate of fallborn, yearling heifers was investigated over 2 consecutive yr. During both years, heifers were stratified by breed (Braford and Brangus-crossbred) and BW and randomly assigned to one of two treatments consisting of 1) wheat middling-based range cube or 2) molasses-cottonseed meal slurry (n = 34 and 24 heifers per treatment for yr 1 and 2, respectively). Supplements were fed at rates to achieve a target of 1.47 and 0.34 kg of supplemental TDN and CP daily, respectively. Four limpograss (Hemarthria altissima) pastures were utilized each year (n = 2 pastures per treatment; 0.71 and 0.51 ha per heifer for yr 1 and 2, respectively). All heifers were allowed free-choice access to stargrass (Cynodon nlemfuensis) hay during periods of limited pasture forage availability. During a 70-d breeding season, heifers were combined by group and exposed to mature Angus bulls. Bulls were rotated among pastures each week. Individual heifer BW and hip height were collected at the start of supplementation and at the start and end of the breeding season. Pregnancy rate was determined by transrectal ultrasonography in late April of each year (minimum of 40 d after the end of breeding). There were no treatment × year, breed × treatment, or breed × year interactions for heifer ADG (P>0.10). Supplement type did not affect heifer ADG (0.44 and 0.47 kg/d for molasses-slurry and range cubes, respectively). Heifers consuming molasses-slurry had a greater (P<0.01) overall pregnancy rate compared with heifers consuming range cubes (76.3% vs 49.2% pregnant). Regardless of treatment, Brangus-crossbred heifers had a greater pregnancy rate (P<0.01) than Braford heifers (73.2% vs 46.8%). These data indicate that yearling heifers supplemented with molasses-cottonseed meal slurry may have increased pregnancy rates compared with heifers supplemented with a wheat middling-based range cube. This response appears to be independent of heifer ADG.

Serum haptoglobin concentration in cattle.

To obtain a basal concentration of serum Haptoglobin (Hp) in cattle in Taiwan, Hp concentrations were measured from serum samples collected from 10 healthy heifers, every week for one year. The values were also compared with those collected from 15 cows diagnosed with postpartum metritis. The heifers were successfully impregnated by artificial insemination six months after the tests. Hp concentrations were also measured in the serum collected from 11 other cows within 3 weeks after parturition. The Hp assay developed in this study gave a good correlation (r=0.893)with Western blotting. The Hp concentration of 454 serum samples from the 10 heifers had a mean value of 83.6 +/- 34.1 mg/l, and there was no significant difference among individual heifers. The basal value of Hp in heifers was calculated as less than 73.6 mg/l. No significant difference in Hp concentration was observed among the 10 heifers during cold and warm seasons (19.8 +/- 2.2 degrees C vs 27.3 +/- 1.4 degrees C), or before and after pregnancy. The mean serum Hp concentration from cows suffering from postpartum reproductive disorders was 1133.5 +/- 627.1 mg/l, which was significantly greater than the serum of healthy heifers and postpartum cows (104.6 +/- 61.0 mg/l) (P<0.05). These results demonstrate that Hp concentration may be a useful indicator for cows with postpartum reproductive disorders.

Supplementation to meet metabolizable protein requirements of primiparous beef heifers: I. Performance, forage intake, and nutrient balance.

Three experiments were conducted to evaluate the response of supplementing primiparous heifers based on the metabolizable protein (MP) system during pregnancy and lactation. In Exp. 1, 12 pregnant, March-calving heifers (432 +/- 10 kg) grazing Sandhills range were randomly allotted to one of two treatments: supplementation based on either the MP system (MPR) or the CP system (CPR). Supplements were fed to individual heifers from October to February and no hay was offered. Grazed forage organic matter intake (FOMI) was measured in November, January, and February. In Exp. 2, 18 heifers (424 +/- 8 kg) were randomly allotted to one of three treatments: 1) supplementation based on the MP system with hay fed in January and February (average 2.0 kg/d; MPR/hay), 2) supplementation based on the CP system, with hay fed in January and February (CPR/hay), or 3) supplementation based on the MP system, with no hay fed (MPR/no hay). Supplements were fed from October to February, and FOMI was measured in December and February. In Exp. 3, lactating 2-yr-old cows (394 +/- 7 kg) maintained on meadow hay were supplemented to meet either 1) MP requirements (LMPR) or 2) degradable intake protein requirements (LDIPR). Body weight (BW) and body condition score change, hay intake, and milk production were measured. In Exp. 1, grazed FOMI decreased (P = 0.0001) from 1.9% of BW in November to 1.2% in February, but no differences among treatments were detected for FOMI or BW change. In Exp. 2, grazed FOMI declined (P = 0.0001) from 1.7% of BW in December to 1.1% in February, with no differences among treatments. Heifers on the MPR/hay and CPR/hay treatments had higher (P = 0.0018) total intake (grazed forage + hay intake) in February (1.7% BW) than the MPR/no hay heifers (1.1% BW). Heifers on the MPR/no hay treatment had a lower weight (P = 0.02) and tended (P = 0.11) to have a lower BCS than heifers on other treatments. In Exp. 3, the LMPR cows had higher (P = 0.02) ADG than LDIPR cows (0.41 and 0.14, respectively), but treatment did not affect milk production. Organic matter hay intake averaged 2.4% of BW. We conclude that supplementation to meet MP requirements had little benefit to heifer performance during gestation, but increased weight change during lactation. Because grazed forage intake decreased from 1.9 to 1.1% of BW with advancing gestation, supplemental energy is necessary to reduce weight and condition loss of gestating hefiers grazing dormant Sandhills range.

Alterations in intrafollicular regulatory factors and apoptosis during selection of follicles in the first follicular wave of the bovine estrous cycle.

Changes in follicular fluid (FF) concentrations of estradiol, inhibin forms, and insulin-like growth factor binding proteins (IGFBPs), percentage of apoptotic granulosa cells (%A), and follicular size for individual follicles in a growing cohort were determined throughout the first wave of follicular development during the bovine estrous cycle and related to FSH decline. Four groups of heifers (n = 31) were ovariectomized between Days 1.5 and 4.5 of the estrous cycle at 5 +/- 1, 33 +/- 2, 53 +/- 1, and 84 +/- 2 h after the periovulatory peak in FSH concentrations. Follicles > or = 2.5 mm were dissected, measured, and FF aspirated. The five largest follicles were ranked based on their diameter (F1 to F5). Diameters of F1 to F5 were positively correlated with interval from FSH peak (r > or = 0.6, P < 0.05). Five hours after the FSH peak, follicular diameter and FF concentrations of estradiol, inhibins, and IGFBPs were similar for F1 to F5. From 5 to 33 h, amounts of the six precursor inhibin forms (> or = 48 kDa) increased (P < 0.05) in F1 follicles. The IGFBPs in F1 follicles remained low at all time periods. At 33 h, amounts of IGFBP-4 and -5 were higher (P < 0.05) in F4 and F5 compared with F1 follicles. At 84 h, IGFBP-2, -4, and -5 were increased (P < 0.05) in F3, F4, and F5 compared with F1. At 5, 33, or 53 h, %A was not different between follicles in any size class. At 84 h %A was increased (P < 0.05) in follicles <6 mm in diameter. However, at that time, %A did not differ between the selected DF and the largest subordinate follicle. For individual heifers, the selected DF at 84 h was largest in size, highest in estradiol, and lowest in IGFBP-2 and -4. The F1 follicle had highest estradiol in 23 of 27 heifers irrespective of stage of the wave and lowest IGFBP-4 in 19 of 21 heifers from 33 h. We concluded that the earliest intrafollicular changes that differentiate a dominant-like follicle from the growing cohort are enhanced capacity to produce estradiol and maintenance of low levels of IGFBPs.

Growth parameters of Holstein-Friesland heifers reared on complete diets containing different roughages

At two months of age, 48 Holstein-Friesland heifers were randomly allocated to four treatments comprising untreated wheat straw (WS), oven-ammoniated wheat straw (AWS), lucerne hay (LH) or oat hay (OH). Least cost nutrient balanced complete diets were formulated for heifers of different age groups, i.e. 2–6, 6–10, 10–13, 13–18 months and 18 months to first calving. Dry matter (DM) intakes of individual heifers were determined twice weekly. Animals were weighed once weekly, and girth circumference and wither height were measured monthly. From 13 months of age, heifers were observed daily for oestrus and inseminated provided that a minimum live weight of 290 kg had been attained. At two months of age, heifers weighed (mean ± s.e.) 69 ± 1.1 kg and wither height and girth circumference measured 84.6 ± 0.4 and 94.1 ± 0.6 cm respectively. The average daily gain of heifers receiving diets containing LH was higher (P < 0.001) from two months of age to calving than that of heifers receiving diets containing WS, AWS or OH (0.76 vs. 0.68, 0.64 and 0.68 kg/day respectively). Heifers receiving LH diets were heavier (P < 0.001) at first calving than heifers fed diets containing other roughages. Wither height at 22 months of age did not differ (P > 0.05) between treatments, the overall mean being 129.3 ± 0.5 cm. Girth circumference of heifers fed diets containing WS, AWS and OH was smaller (P < 0.001) than that of heifers fed LH (179.2, 177.3 and 176.7 cm vs. 188.3 cm respectively). Heifers fed diets containing LH also had higher (P < 0.01) condition scores than heifers fed diets containing other roughages. The lower feeding cost of AWS diets in comparison to other diets should be utilized fully in the rearing of replacement heifers. (South African Journal of Animal Science, 2000, 30(2): 121-127)

Optimal heifer management decisions and the influence of price and production variables

A dynamic programming model was developed to optimize the rearing strategy of individual heifers. The model optimized management decisions with respect to growth rate, insemination and replacement by maximizing the present value of net returns per heifer place. Faced with the scarcity of exact information on the fundamental elements of heifer rearing, sensitivity analyses were carried out to evaluate the technical and economic consequences of various price and production variables. Results for Dutch conditions showed that it was most profitable to rear heifers at the highest achievable growth rates without fattening. Based on a critical prepubertal average daily gain (ADG) of 900 g/day and a maximum achievable postpubertal ADG of 700 g/day, optimum policy resulted in an average age of first calving of 21.2 months at a body weight of 541 kg. The sensitivity analyses demonstrated a considerable impact of the critical prepubertal growth rate on both the optimal rearing policy and expected net returns. Technical and economical results were also very sensitive to seasonal influences on price and production variables. Heifer calves born in winter were the most profitable calves to rear.

Economic optimization of dairy heifer management decisions

A farmer exercises control over the heifer rearing unit in two main areas: a nutritional plane of growth and the moment of insemination. The two management controls interact with biological aspects of growth thereby influencing future profitability of the dairy heifer. A dynamic programming model was developed to optimize these decisions for individual heifers, using the hierarchic Markov process (HMP) technique. HMP provides a method to model a wide variety of heifer calves, differing in age, season, body weight, reproductive status and prepubertal growth level. Under Dutch conditions the optimal rearing strategy resulted in an average calving age of 22.6 months at a calving weight of 564 kg. Faced with the scarcity of exact information on the interrelationships of rearing strategies with the productivity of the dairy replacement, the strength of this heifer model lies in the field of the sensitivity analyses by providing valuable information regarding the critical components of heifer rearing.

Repeatability of ultrasound-predicted percentage of intramuscular fat in feedlot cattle.

We used data from 144 bulls, heifers, and steers to determine the repeatability of ultrasound-predicted percentage of intramuscular fat and to study the effect of repeated measurements on the standard error of prediction. Animals were scanned at an average age of 433 d by a certified technician. Individual bulls, heifers, and steers were scanned five to six times each with two Aloka 500-V machines, and the percentage of intramuscular fat was predicted from two regions of interest within an image. Variance components and repeatability values were computed for the overall data and by machine, region of interest, and sex. Animals were broadly divided into two groups based on mean ultrasound-predicted percentage of intramuscular fat. Variance components and repeatability values were then estimated within each group. The overall repeatability of ultrasound-predicted percentage of intramuscular fat was .63 +/- .03. Differences in the repeatability values between machines and between regions of interest were not different from zero (P > .05). Bulls showed a lower within-animal SD of .82% as compared to .97 and 1.02% for steers and heifers, respectively. However, steer ultrasound-predicted percentage of intramuscular fat measures were more repeatable (P < .05) than those of bulls and heifers. The difference in repeatability between bull and heifer measures was not important (P > .05). Animals with mean ultrasound-predicted percentage of intramuscular fat less than 4.79% showed less repeatable measures (P < .05) than those with means above 4.79%. The image variance contributed to nearly 70% of the total variance of observations within an animal. Standard error of animal mean measures showed a 50% reduction when the number of images per animal increased to four. Therefore, we concluded that increasing the number of images per animal plays a more significant role in reducing the standard error of prediction than taking multiple measurements within a single image.

Surges of FSH during the follicular and early luteal phases of the estrous cycle in heifers

Surges of FSH were characterized in each of 12 Holstein heifers using a computerized cycle detector program, and as mean changes averaged over all heifers. Blood samples were collected 6 times a day at 4-h intervals beginning at late diestrus. Concentrations of FSH were adjusted relative to the preovulatory LH peak (Hour 0) and profiled beginning 48 h before and ending 120 h after the LH peak. Peak concentrations of FSH and LH occurred synchronously in 11 of 12 (92%) heifers, and only a 4-h interval separated peak concentrations in the remaining heifer. The FSH surge that was synchronous with the LH surge was designated FSH Surge 1 and was used as a reference to designate other FSH surges. Surge −1 of FSH was detected in 58% of the heifers at mean Hour −21.2, and Surges 2, 3 and 4 were detected in 92%, 92% and 75% of the heifers, respectively, at mean Hours 25.1, 57.8 and 78.7. Mean peak levels and duration of FSH Surges-1, 2, 3 and 4 were significantly lower than for FSH Surge 1. Mean concentrations of FSH significantly increased and decreased before and after the LH peak, resulting from the synchrony between FSH Surge 1 and the LH surge in individual heifers. Additionally, there was a tendency (P < 0.08) for a second and third increase in mean FSH concentrations at Hours 24 and 60, which was attributed to FSH Surges 2 and 3 that occurred in individuals. Peak FSH concentrations of Surge 2 occurred (mean, Hour 25.1) within 8 h of maximal mean concentrations at Hour 24 in 91% of the heifers. Correspondingly, peak FSH concentrations of Surge 3 occurred (mean, Hour 57.8) within 8 h of maximal mean concentrations at Hour 60 in 64% of the heifers. Surges −1 and 4 of FSH occurred less frequently and at various times within and among heifers compared with Surges 1 to 3; therefore, they were not detected as mean increases in FSH concentrations but were masked as a result of concentrations being averaged over all heifers. In summary, FSH surges were detected in individual heifers before and after the combined FSH/LH surge. The interpeak intervals for FSH Surges 1 to 2 (25 h), 2 to 3 (33 h) and 3 to 4 (21 h) suggests a rhythmic nature to the surges.

Genetic Analysis of Growth Patterns of Black and White Dairy Heifers

Monthly BW to 600 d of age along with BW at first calving of 743 heifers were analyzed to estimate the genetic relationship between BW at first calving and other growth variables. The Von Bertalanffy function and a two-phase logistic function were used to fit growth patterns of individual heifers. The two-phase logistic function fitted the data more adequately than did the Von Bertalanffy function. Calves from first parity dams were born at a lower degree of maturity than calves from third parity dams. Calves with a high proportion of Holstein genes had a higher BW both at first calving and at maturity. Heritabilities of the variables of the Von Bertalanffy and the two-phase logistic function ranged from 0.02 to 0.31 and 0.15 to 0.26, respectively. Estimated mature BW had a highly negative correlation with rate of maturation (–0.56 to –0.82); BW at first calving had a high genetic correlation (0.74 to 0.90) with estimated mature BW and a negative correlation with maturation rate (–0.18 to –0.40). Results of this study indicated that BW at first calving can be used as an indirect trait when mature BW is included in the breeding goal.

Calcium involvement in luteinizing hormone-releasing hormone release from the bovine infundibulum

Bovine infundibular (stalk median eminence) explants were incubated in vitro to test the hypothesis that calcium (Ca) is involved in the release of luteinizing hormone-releasing hormone (LHRH) from LHRH neuron terminals in cattle. Right and left infundibular halves from individual heifers and/or steers were randomly assigned to either control or treated (EGTA [a Ca chelator] or verapamil [an L-type Ca channel antagonist]) groups. Each half was incubated in 600 μl of KrebsRinger bicarbonate medium (KRB) in the presence or absence of a treatment agent for 180 min. At 30-min intervals, 500-μl samples were removed from each incubate and replaced with fresh media. Spontaneous (basal) and depolarization-induced (60 mM potassium) LHRH release was evaluated by radioimmunoassay of the LHRH content in the media incubated from 91 to 120 and 121 to 150 min of culture, respectively. The effect of treatment on depolarization-induced LHRH release was analyzed by comparing the differences between spontaneous and depolarization-induced LHRH release in control and treated groups. Spontaneous LHRH release was not different between control and 1.25 mM EGTA- or 100 μM verapamil-treated halves from steers. In contrast, steer infundibular halves incubated with EGTA (replacing Ca in KRB and chelating any Ca in the media) released less LHRH during depolarization than did control halves. In addition, verapamil-treated (to block Ca uptake by the terminal) infundibular halves from steers or heifers released less LHRH in response to depolarization than did control halves. In conclusion, these results: 1) support the hypothesis that Ca is involved in LHRH release from the bovine infundibulum, 2) suggest that the involvement of Ca may be independent of the reproductive state, and 3) demonstrate that bovine infundibular halves incubated in vitro are useful for studying selected mechanisms regulating bovine hypothalamic neurohormone release (exocytosis) from neuron terminals.

Penicillin G and penicillin G-tinidazole treatment of experimentally induced summer mastitis — effect on elimination rates of bacteria and outcome of the disease

Two udder hind quarters of ten pregnant heifers were inoculated experimentally with a combination of Actinomyces pyogenes, Peptostreptococcus indolicus and Fusobacterium necrophorum at a dose of 9×10 8 colony forming units (CFU) of each species of bacteria. The development of aerobic-anaerobic mastitis was followed-up clinically and through analysis of udder secretion samples. All heifers developed acute clinical mastitis. Thick, purulent secretions with foul odour were already present 24 h after infusion. At 32 h post inoculation, 19 of 20 quarters harboured all infused bacteria, the viable counts of bacteria varying from 10 4 to 10 5 CFU/ml. No bacteria were isolated from blood samples taken simultaneously. NAGase values of udder secretions, indicating tissue damage, were high. The heifers were treated systemically with penicillin G alone, or in combination with tinidazole. Treatment started 32 h after inoculation and was continued for three days. The anaerobic bacteria ( F. necrophorum and P. indolicus) were usually eliminated within four days, while A. pyogenes infections often persisted in the quarters. Penicillin G with tinidazole was not more effective than penicillin G alone: of the four heifers which recovered from infection, two were treated with penicillin G alone and two with the drug combination. The most important factor affecting the recovery seemed to be the host response of individual heifers. The six heifers which did not recover from the infection were continuously infected after calving, harbouring A. pyogenes in ten quarters, and P. indolicus and F. necrophorum each in three quarters.