BMY牛提前产犊试验

[目的]为提高母牛的利用年限、缩短后备母牛的培育时间、探索BMY青年牛的适配年龄（体重）和提前妊娠产犊对母畜和犊牛的影响。[方法]对断乳母犊进行适当培育,使其早进入初情期,运用繁殖生物技术妊娠产犊。[结果]经过培育后BMY青年牛的初情期平均为（270.8±20.8）d,此时的平均体重为（254±10.6）kg,发情周期...     

Effect of calflhood morbidity on age at first calving in New York Holstein herds

The effect of calhood morbidity on age at first calving was investigated in 948 heifer calves in 21 herds in the vicinity of Cornell University. Heifers were born from July 1983 to April 1985 and neither died nor were sold prior to 90 days of age. All calvings occurred on or before 31 May 1987.

The specific calfhood morbidity variables of interest were the first occurrences of the following clinical signs as diagnosed by farmers on check-off forms: scours/diarrhea within 14 days of birth and from 15 to 90 days of age; dull, listless, droopy ears, or off of feed within 90 days of birth; cough, runny nose or eyes, or trouble with breathing within 90 days of birth. The Kaplan-Meier product-limit life-table technique and Cox's proportional hazards model were used to evaluate the effect of calfhood morbidity on the age distribution of first calving. Season and year of birth were included (forced) into the Cox's proportional hazards model as possible confounding variables. The model was stratified on herd (allowing a different survival function for each herd) in order to account for herd effects.

The final Cox's proportional hazards model included season and year of birth, signs of respiratory illness within 90 days of birth and dullness within 90 days of birth. Heifers without respiratory illness as calves were twice as likely subsequently to calve and calved 6 months earlier when compared to those with respiratory illness as calves. Heifers with dullness as calves were 1.6 × more likely to calve and calved 2 months earlier when compared to calves without dullness as calves.     

Genetic and Environmental Correlations Among Female Fertility Traits and Milk Production in Different Parities of Swedish Red and White Dairy Cattle

The main objective of this study was to estimate genetic correlations between fertility and production traits in first, second and third lactations as well as between fertility traits measured in the same way at different ages. The fertility traits studied were: number of inseminations per service period, number of treatments for reproductive disturbances, interval between first and last inseminations, interval between calving and first insemination, and interval between calving and last insemination. Early milk production was measured as the average of the energy-corrected milk yield at the second and third monthly testdays in a lactation. The number of records was approximately 450 000, 350 000, 180 000 and 75 000 in the heifer period, first, second, and third lactations, respectively. A linear, trivariate model that included the effects of herd-year, year, month, age and sire of the cow was applied. To reduce the effect of ongoing selection, 305-days kg protein production in first lactation was included as a variate in all of the analyses. Correlations between the herd-year effects indicated that factors of herd-year level conducive to increased production had a tendency to increase the number of inseminations as well as the number of reproductive treatments, although there was an earlier start and termination of the insemination period. Genetic correlations between fertility traits and production were in the range of 0.2-0.4, all of them unfavourable and higher at later parities. The genetic correlations between fertility traits in the heifer period and the same traits in first lactation were 0.7. Genetic correlations between the first and second lactation varied between 0.7 and 0.9, and between the second and third lactation they were all 0.9 or higher. In conclusion, fertility and production traits need to be selected for simultaneously if fertility is going to be maintained along further genetic improvement on production, and such selection should include fertility results from lactating cows.     

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.     

Effect of polymorphisms at the STAT5A and FGF2 gene loci on reproduction, milk yield and lameness of Holstein cows

The objective of this study was to investigate the association of polymorphisms at the STAT5A and FGF2 gene loci with fertility, lactation milk yield and lameness in dairy cattle. Five hundred and eighteen primiparous Holstein cows were included in the study. Several reproductive traits were considered including conception rate (0/1) at first insemination, conception rate (0/1) in a 305-day lactation, number of inseminations per conception, interval (days) from calving to conception for cows that conceived in the first 305 days of lactation and age at first calving. Milk yield and lameness incidence were also recorded. Genotyping was performed using PCR-RFLP. The effect of allele substitution at each gene locus on reproductive traits, milk yield and lameness was assessed with single-trait mixed linear models. No significant associations were found between reproduction traits and any of the studied polymorphisms, apart from age at first calving, for which STAT5A polymorphism had a suggestive effect (P = 0.077). In addition, no significant effect of any polymorphism on lameness was found. Replacement of the C by G allele at the STAT5A locus was associated with a significant (P < 0.05) increase in lactation milk yield, suggesting that this locus could be considered in gene assisted selection for the genetic improvement of milk production.     

Analysis of gestation length in American Simmental cattle

Records of gestation length (71,461) for Simmental cattle were distributed with mean 284.3 d and standard deviation 5.52 d. Gestation length was found to increase with percent Simmental and was 1.9 d longer for calves born to mature dams than for those born to heifer dams. Bull calves experienced gestation lengths 1.5 d longer than heifer calves. Sire, maternal grandsire, residual and total variances were estimated to be 2.42, .58, 22.78 and 25.78 d2, respectively, by Henderson's Method III. Heritability of gestation length was calculated to be .374 from the sire variance and .09 from the maternal grandsire variance. Direct additive genetic variance was considered to be of greater importance than maternal additive genetic variance. Correlations between the evaluations of sires for gestation length and heifer calving ease, birth weight and weaning weight were .26, .26 and .13, respectively.     

Dam-related effects on heart girth at birth,morbidity and growth rate from birth to 90 days of age in Swedish dairy calves

We investigated the effects of dam-related factors (such as calving performance, milk leakage, diseases, milk production, and somatic-cell count (SCC)) on heart girth at birth and the incidence risk of diarrhoea and respiratory disease during the first 90 days in Swedish dairy calves. The effects of these dam-related factors and environmental and management-related (but not dietary) factors on the calves' growth rate during the first 90 days of life also were analysed. The study used nearly 3,000 heifer calves born in 1998 on 122 farms in the south-west of Sweden. Individual health records were kept by the farmers and visiting project veterinarians. The calf's heart girth was measured at birth and weaning. We used generalised linear mixed models for the size of the calf at birth and growth rate. Variables associated with the heart girth at birth were breed, calving performance, mastitis in the dam in the last 49 days before calving, milk production and parity. Variables associated with the growth rate were breed, calving performance, disease in the calf during its first 90 days of life, heart girth at birth, and housing of calves. The effect of the dam on the relative risk of diarrhoea and/or respiratory disease in the calf was evaluated by a generalised linear mixed model with a logit link. Morbidity in the dam during late pregnancy, retained placenta and SCC were associated with the relative risk of respiratory disease in the calf. None of the explanatory variables (other then breed) was associated with the relative risk of diarrhoea.     

Reproductive performance in the subsequent lactation of dairy cows previously treated for failure to be detected in oestrus

AIM: To describe the effect of treatment of cows not detected in oestrus (NDO) with progesterone (P4) and oestradiol benzoate (ODB) in one lactation, on the reproductive and productive performance in the subsequent lactation. METHODS: Cows (n=770 from nine herds) which were NDO 10 days before the planned start of the seasonal breeding programme (PSM) were blocked by herd, age (2 or >2 years old) and ovarian status (i.e. with or without a palpable corpus luteum; CL), and treated either with an intravaginal progesterone-releasing device and ODB and resynchrony, or were left as untreated controls. In the following lactation, data were collected on the occurrence of endometritis, NDO, breeding dates, pregnancy test results and milk production. The effect of treatment and ovarian status in the previous lactation on the incidence of disease, and the proportions submitted for service, conceived and pregnant in the subsequent lactation were analysed. Calving dates and intervals from start of breeding to first insemination and conception were analysed using Kaplan Meier survival analysis. Additional multivariate analyses were undertaken to include known confounders such as age, breed, herd, calving date and milk production, as well as the cyclic status (i.e. previously cycling, NDO, or "late-calving") in the previous lactation, to examine the potential "carryover" effects of previous status on the reproductive performance in the subsequent lactation. RESULTS: Treatment of NDO cows resulted in an earlier calving date (Julian calving date 214, 95% CI=207-221, vs 224, 95% CI=220-228; p=0.005), more female calves reared (31.4% vs 23.3%; p=0.01), and reduced risk of being NDO (33.9% vs 46.1%; p=0.002) in the subsequent lactation compared with controls. There were no differences in the incidence of peripartum disease, or the proportion of cows submitted, conceived or pregnant between the Treatment and Control groups in the subsequent lactation (p>0.2). Previously CL-positive (+ve) NDO cows were less likely to produce a female calf that was reared (19.0% vs 29.9%; p=0.005), more likely to be treated as NDO (26.4% vs 18.6%; p=0.02), less likely to conceive by the end of the subsequent lactation's breeding programme (82.2% vs 87.8%; p=0.09), and took longer to conceive (41 vs 33 days from the PSM to conception) than cows that were NDO-CL-negative (-ve) in the previous lactation. There was no interaction between ovarian status and treatment for any of the outcome variables (p>0.05). Cows that were NDO or late-calving in the previous lactation were more likely to be NDO (p<0.005), treated as NDO (p<0.005), and have longer PSM to conception intervals (p<0.005) in the subsequent lactation than cycling herdmates, despite inclusion of factors known to confound reproductive performance in analyses. CONCLUSIONS: Treatment of NDO cows resulted in more female calves reared, earlier calving and a reduced risk of being NDO in the subsequent lactation. Status (i.e. NDO-CL+ve or NDO-CL-ve) affected some reproductive measures in the subsequent lactation, and the effect of treatment in the subsequent lactation differed between the two groups for some measures. Reproductive performance in the subsequent lactation was not improved despite the earlier calving date and longer calving to PSM intervals. Additionally, the previous season's status was still important in the subsequent season's reproductive performance, despite adjusting for known confounders of fertility. CLINICAL RELEVANCE: The economic benefits from treatment of NDO cows are likely limited to effects of an earlier calving date and potential for longer lactation and increased milk yield, increased number of calves derived from artificial insemination and from a reduced number of NDO cows in the subsequent lactation. Effects of improved reproductive performance in the subsequent lactation were not demonstrated and hence should not be included in any economic analysis of therapy of NDO cows.     

Growth,reproductive, and productive performance of Begait cattle under different herd management systems in northern Ethiopia

The performance of indigenous Begait cattle (498 cows, 284 calves, and 48 heifers) in northern Ethiopia was studied. System of herd management significantly (P?<?0.01) influenced all production traits. Calves in medium-input herds (MIHM) grew faster than those in low-input herds (LIHM), by 232 g/d from birth to 9 months (Gain₁) and by 385 g/d from 9 to 12 months (Gain₂). Cow’s dry period, calving interval (CI), and age at first calving (AFC) were 234, 222, and 343 days shorter for MIHM than for LIHM. Compared with LIHM, cows from MIHM had 74% higher daily milk yield (DMY) and 91% higher lactation milk yield (LMY). Calves born at wet season grew faster by 14 and 10% than those calves born in the dry season at Gain₁ and Gain₂. The subsequent CI of cows calved in the wet season had 77 days shorter, 0.45 kg DMY, and 93 kg LMY increment. The differences between production systems can be attributed to differences in management skills and access to better quality feeds. Technical intervention is needed to ensure provision of balanced rations to exploit the potential productivity of Begait cattle.     

Effect of birthweight, total protein, serum IgG and packed cell volume on risk of neonatal diarrhea in calves on two California dairies.

The objective of the study was to determine if there was a relationship between hematological, immunological and physiological variables of newborn calves and risk of diarrhea during the neonatal period. Four hundred and seventeen heifer calves from two dairies (A and B) in the San Joaquin Valley of California were enrolled at birth and scored daily, to 28 days of age, for evidence and severity of diarrhea (0 to 3). Calves were weighted at birth and blood sampled at two to five days of age to determine packed cell volume (PCV), total protein (TP) and IgG serum concentration. The Cox proportional hazards model was used to determine if age at onset of the first diarrhea episode and length of the first episode were associated with the hypothesized variables (PCV, TP, IgG and birthweight). The IgG concentration was not associated with the age at onset of diarrhea (p = 0.6052, Dairy A; p = 0.4393, Dairy B) but a high IgG concentration was associated with a decreased length of episode (p = 0.0325, Dairy A; p = 0.0912, Dairy B), particularly for calves born in the winter on dairy A (p = 0.0211). For calves born in the winter, those with either a high or a low birthweight had diarrhea at a younger age (p = 0.0102, Dairy A; p = 0.0020, Dairy B). Associations were also found for PCV and TP with both the age at onset and length of the first episode of diarrhea. Results suggest that parameters measurable at, or shortly after birth may have important prognostic value in evaluating risk of calf diarrhea.     

Body measurements of newborn calves and relationship of calf shape to sire breeding values for birth weight and calving ease

Body measurements on Angus- (n = 374) and Polled Hereford-sired (n = 438) calves were used to quantify calf shape via multivariate factor analysis, and measurements on Polled Hereford-sired calves were further used to investigate relationships between calf shape and sire expected progeny differences (EPD) for birth weight and first-calf calving ease. Calf birth weight, head circumference, shoulder width, hip width, heart girth, cannon bone circumference and length, and body length were recorded at 24 h postpartum. Sire birth weight EPD was positively associated (P less than .05) with all calf measures but only with head and cannon circumference after adjustment for phenotypic birth weight and gestation length. Thus, at constant birth weight, calves from higher birth weight EPD bulls tended to have larger cannon and head circumferences. Calving ease EPD was negatively related (P less than .05) to all calf measures except shoulder width. After adjustment for birth weight, only cannon circumference was associated with calving ease EPD, and this effect was removed by additional adjustment for birth weight EPD. Thus, at constant birth weight, bulls with higher EPD for calving ease sired calves with smaller cannon circumference, but at constant birth weight EPD, body measures were not associated with calving ease EPD. Factor analysis defined underlying skeletal width and frame components of shape (independent of birth weight) for both sire breeds. Calf shape differed among sires and was in part explained by birth weight EPD. No additional variation in shape was explained by calving ease EPD. Calf shape seemed to add no information for prediction of dystocia to that provided by birth weight EPD.     

Reproductive rates, birth weight, calving ease and 24-h calf survival in a four-breed diallel among Simmental, Limousin, Polled Hereford and Brahman beef cattle

Calving and weaning rates, birth weight, calving ease, and 24-h calf survival were evaluated in a four-breed diallel of Simmental (S), Limousin (L), Polled Hereford (H) and Brahman (B) beef cattle in five calf crops. Limousin dams tended to have the highest calving and weaning rates because they were able to have heavier calves with less calving difficulty and higher survival rates. Brahman-sired calves were the heaviest at birth (P less than .05) and B dams produced the lightest calves (P less than .001). Lower birth weights tended to be the limiting factor on survival of these calves. A linear comparison among means to evaluate purebred, additive, maternal and specific combining ability effects showed most of the reduction in birth weight from B dams was due to maternal effects. Breed of dam accounted for a higher proportion of variation in calving ease than did sire breed. Simmental sires had significantly heavier calves at birth and S and H dams tended to have more calving difficulty and lower survival rates. Heterosis for these traits was generally not significant. Correlations were generally positive and significant for birth weight and calving ease, but were more variable for birth weight and survival. Linear regressions of calving ease on birth weight both within years and within dam-breed-year subclasses were very similar in that the association of these two traits was reduced as dam age increased.     

Bovine embryo transfer pregnancies. I. Abortion rates and characteristics of calves

Data were obtained from 1,908 pregnancies resulting from bovine embryo transfer procedures. Responses examined included sex ratio, fetal, neonatal and preweaning death losses, birth weight and calving assistance. The sex ratio for 1,751 embryo transfer calves examined was 51.11% males. Cows older than 10 yr that had become repeat breeders produced more (P less than .05) male calves than other donors. Breed of embryo, age and quality of embryos at the time of transfer, embryo storage time from collection to transfer, asynchrony of recipient with donor estrus and number of palpable corpora lutea in superovulated donors were not related to sex ratio (P greater than .05). The abortion rate between 2 and 3 mo of gestation in embryo transfer recipients was 3.15%, and between 3 to 7 mo, 2.14%. Neonatal and preweaning losses for 1,682 calves with complete information were 1) congenital defects, .54%; 2) death due to premature birth (7 to 8 mo of gestation), .18%; 3) dystocia-related deaths, 2.38%; 4) deaths of unknown causes at birth, 2.14%; 5) deaths of unknown causes from 24 h after birth to weaning, 1.43%; 6) deaths due to calfhood diseases, 1.25% and 7) deaths due to environmental factors, 1.13%. Total losses of 2-mo pregnancies due to abortion or death of calves or recipients were 14%. Birth weight of embryo transfer calves changed .29 kg/d of deviation from average gestation length (P less than .005) for pregnancies within breeds. Birth weight was also affected (P less than .005) by donor breed and recipient breed and age. Male calves averaged 2.19 kg heavier (P less than .005) than females. Calving assistance was affected by donor breed; Angus calves required the least assistance (P less than .005). Hereford, Holstein and Limousin calves were similar and intermediate; Simmental calves needed the most calving assistance. Recipient breed and age influenced calving ease, with younger recipients of Angus and Hereford descent requiring more assistance (average calving score, 2.1) than both cow (1.3) and heifer (1.5) recipients of the larger Continental European breeds. Characteristics of 305 non-embryo transfer calves were not significantly different from 185 embryo transfer calves from the same farms. We conclude that embryo transfer calves did not differ from the non-embryo transfer population in any of the characteristics studied.     

Morbidity in Swedish dairy calves from birth to 90 days of age and individual calf-level risk factors for infectious diseases

The health of 3081 heifer calves born in 122 dairy herds in the south-west of Sweden from 1 January to 31 December, 1998, was monitored from birth until 90 days of age. The calves were kept either in individual pens (n=2167), in group pens, with 3–8 calves to a pen and manual feeding of milk (n=440), in group pens with 6–30 calves per pen and an automatic milk-feeding system (n=431), or with their dams (n=43). Disease incidence was recorded by farmers and project veterinarians, who clinically examined the calves and auscultated their lungs every 2–3 months. A disease was graded as ‘severe’ if the general loss of condition or of appetite in the calf continued for >2 days or if the animal suffered severe weight loss due to the disease. The effects of season, breed, housing, and type of colostrum feeding, and time, place and supervision of calving on the incidences of diarrhea, severe diarrhea, respiratory disease, other infectious disease and moderately to severely increased respiratory sounds, were analyzed by logistic-regression models (with herd as a random effect). The total morbidity rate was 0.081 cases per calf-month at risk. Incidence rates of arthritis, diarrhea, omphalophlebitis, respiratory disease and ringworm were 0.002, 0.035, 0.005, 0.025 and 0.009 cases per calf-months at risk, respectively. The odds ratios for diarrhea and severe diarrhea were increased in Swedish Red and Whites (OR: 1.6, 2.3) and in calves that received colostrum from first-lactation cows (OR: 1.3–1.8), and for severe diarrhea in calves born in summer or that received colostrum through suckling (OR: 1.7, 1.8). The odds ratios for respiratory disease and increased respiratory sounds were increased in calves housed in large-group pens with an automatic milk-feeding system (OR: 2.2, 2.8). Supervision of calving was associated with a decreased odds ratio for respiratory disease (OR: 0.7) and birth in individual maternity pen or tie stalls with a decreased odds ratio for increased respiratory sounds (OR: 0.5–0.6). Cross-breeds with beef breeds were associated with increased odds ratios for increased respiratory sounds (OR: 2.1–4.3) and colostrum from second-lactation cows and birth during night for other infectious disease (OR: 1.6, 1.5).     

Techniques for estimation of milk yield in beef cows and relationships of milk yield to calf weight gain and postpartum reproduction

Milk production is a primary factor controlling weaning weight of beef calves. The purpose of this experiment was to develop a practical and reliable on-farm method of estimating milk production and to relate estimates of milk production and milk composition to preweaning weight gain of calves. A second objective was to relate milk production to postpartum ovarian activity. Milk production of spring- and fall-calving grade Angus cows was estimated by machine milking (MM; average of 66, 123 and 189 d postpartum) and weigh-suckle-weigh (WSW; average of 50, 95, 136 and 179 d postpartum) techniques following overnight calf removal. Cows and calves were weighed monthly and the postpartum interval to first ovulation following calving was determined. The repeatability of the estimated milk production by MM (.97) was higher (P less than .01) than by WSW (.35). The correlation of average WSW and average MM estimates of milk production with preweaning calf gain were high and similar (greater than .75). Inclusion of milk composition did not improve the multiple correlation of MM-estimated milk production and calf gain. Neither milk production in early lactation (-.06) nor prebreeding weight change (-.07) was correlated with postpartum interval to ovulation. Machine milking was a repeatable method of estimating milk production of beef cows and can be used to evaluate effects of management variables on lactation of beef cows.     

Calf growth in captive Iberian red deer (Cervus elaphus hispanicus): effects of birth date and hind milk production and composition

This study examines effects of birth date, hind milk production and its composition, and weight of hind and calf at birth (HBW and CBW, respectively) on calf growth responses born to Iberian hinds (Cervus elaphus hispanicus) and lactating over 34 wk. Males showed daily gains greater than those of females (P = 0.04). Calf birth weight was strongly related to calf gain over a standard (15-wk) lactation (P < 0.01), but HBW did not influence growth or CBW (P > 0.10). After correcting for nutrient supply, birth date did not affect growth, but birth date x total protein yield (TPY), birth date x total fat yield (TFY), and birth date x total lactose yield (TLY) interactions influenced growth (P < 0.001), and early-born calves showed greater growth than those born late for wk 2 to 34 (P < 0.05). Calf birth weight showed the highest correlation with protein-to-fat ratio in milk (P < 0.001), a high correlation with milk protein content (P < 0.05), and a low negative correlation with fat (P < 0.10). Calf gains also showed the highest correlation with protein-to-fat ratio in milk (P < 0.05). Similarly, total milk yield (TMY), TPY, and TFY during lactation affected growth as single factors (P < 0.001). Calves showed not only an overall difference in daily gain between calves born early or late (P = 0.02), but also a greater speed of growth independently of CBW (percentage of weight gained per week, P < 0.001). Early-born calves were heavier at 12 and 18 mo (P < 0.05). Results suggest that selecting hinds of high milk production and nutrient supply and advancing calving date may increase growth of calves and their performance at adulthood.     

Body measurements of crossbred calves sired by Simmental bulls divergently selected for progeny first-calf calving ease in relation to birth weight

Simmental bulls (n = 27) were divergently selected on linear model first-calf calving ease expected progeny difference (CEPD) relative to birth weight expected progeny difference (BEPD) so that body measures of calves from sires whose progeny tended to be born either with more or less dystocia than expected from BEPD could be obtained. At birth, calf weight, head circumference, shoulder width, hip width, heart girth, cannon bone circumference and length, and body length were recorded for 204 calves. These measures had also been obtained from the Polled Hereford X Angus dams of the calves at their births. Sire differences (P less than .05) existed for calf cannon bone circumference and length before and after adjustment for gestation length and birth weight of the calf. Sire BEPD was positively associated with cannon and head circumferences independent of phenotypic birth weight and gestation length. No relationship existed between CEPD or threshold model first-calf calving ease expected progeny difference and any calf measure, either before or after adjustment for birth weight. Multivariate factor analysis was used to describe independent components of skeletal width, frame, and thickness after removal of birth weight effects; factors were not related to genetic merit for calving ease or observed calving performance. Independent of weight, newborn calf measures were not highly related to body measures at weaning or to dam birth measures. Body shape differences at constant weight existed in crossbred calves, but they were not related to sire genetic merit for calving ease or measured dystocia. Selection for calf body shape, independent of birth weight, would not reduce dystocia.     

Genetic (co)variances for calving difficulty score in composite and parental populations of beef cattle: II. Reproductive, skeletal, and carcass traits

There is limited genetic information relating calving difficulty and body weights to other productive and reproductive traits. Such information is useful for specifying selection criteria and for predicting economic consequences of selection. Genetic, maternal, and environmental covariances of six productive and reproductive measurements with calving difficulty, birth weight, 200-d weight, and 168-d postweaning gain were estimated in 12 experimental populations of cattle. Calf (direct) genetic effects resulting in longer gestation length were associated with increased calving difficulty and birth weight. Maternal genetic effects of increased gestation length and heavier birth weight were significantly associated. Lighter birth weight and reduced calving difficulty were associated with earlier heifer age at puberty. Increases in direct genetic effects of calving difficulty, 200-d weight, and postweaning gain were associated with a small increase in direct effect of scrotal circumference. Increased direct genetic effects of scrotal circumference were correlated with maternal effects decreasing calving difficulty and increasing 200-d weight. Direct effects of the skeletal measurements, yearling hip height, and heifer pelvic area were positively correlated with direct effects of calving difficulty, birth weight, 200-d weight, and postweaning gain, positively correlated with maternal effects for birth weight and 200-d weight, and negatively correlated with maternal calving difficulty. Percentage of retail product was positively associated with calving difficulty and negatively associated with 168-d gain. Predicted genetic change in calving difficulty resulting from one standard deviation of selection for either calving difficulty score or birth weight was much larger than for any other traits. Selection for 200-d weight, 168-d postweaning gain, hip height, pelvic area, or scrotal circumference was predicted to have opposite effects on direct and maternal calving difficulty. Estimated genetic correlations indicate some small to moderate relationships between calving difficulty and the measured productive and reproductive traits. However, selection for reduced calving difficulty should be based on calving difficulty score and(or) birth weight because of their superiority in predicted genetic change.     

Milk yield and lactation length of Ghana Sanga and its crosses with the Friesian Raised under agropastoral system

Milk yield traits and lactation length of two breeds of cattle raised on natural pasture with little or no supplementation were assessed. A total of 42 573 daily milk records on 98 Friesian-Sanga cows collected over a period of 10 years and 17 790 daily milk records on 72 Sanga cows spanning a 6-year period were used in the study. Traits examined for each breed were daily milk yield, total milk yield, 305-day milk yield, 305-day milk yield/day and lactation length. Friesian-Sanga cows outperformed their Sanga counterparts in all traits studied. Friesian-Sanga cows had an average daily milk yield of 1.35?±?0.00 kg; average total milk yield of 266?±?12 kg; average 305-day milk yield of 339?±?10 kg; average 305-day milk yield/ day of 1.11?±?0.03 kg and mean lactation length of 201.1?±?6.9 days. Average values for Sanga cows were 1.01?±?0.00 kg as daily milk yield; 162?±?12 kg as total milk yield; 244?±?10 kg as 305-day milk yield; 0.80?±?0.03 kg as 305-day milk yield/day. Mean lactation length for Sanga cows was 164.1?±?9.4 days. Season of calving significantly (P?<?0.05) influenced daily milk yield of Friesian-Sanga cows and all traits of Sanga cows with animals calving in the major rainy season surpassing those that calved in the minor and dry seasons. Daily milk yield for both Friesian-Sanga and Sanga cows was significantly (P?<?0.05) influenced by season of lactation. Daily milk yield gradually declined from second parity towards the sixth parity for Friesian-Sanga cows. A gradual increase in daily milk yield from first to third parity was observed in Sanga cows. Year of calving significantly influenced all traits for both breeds. Genetic improvement in milk yield traits and lactation length is achievable for both breeds of cattle as co-efficient of variation of traits were moderate to high.     

Production characters of primiparous females of a five-breed diallel

Data included pubertal, reproductive and lactation records of primiparous females produced in a diallel of Angus, Brahman, Hereford, Holstein and Jersey. Brahman heifers were oldest, tallest and heaviest at puberty, while Jersey heifers were youngest, shortest and lightest. Crossbred heifers were 22 d younger (P less than .01) at puberty than straightbred heifers; no significant differences were detected between the two groups for weight or height at puberty. Dairy heifers (Holstein and Jersey) required fewer services (P less than .05) to conception than beef heifers. The difference between straightbred and crossbred heifers for number of services to conception was small and nonsignificant. Rank of straightbreds for age at conception was similar to their rank for age at puberty except that Holstein required 1.2 fewer services and were younger at conception than Jersey. Crossbreds were 41 d younger (P less than .05) at conception than straightbreds. Brahman had the longest gestation length and were oldest at first calving; Jersey had the shortest gestation length and Holstein were youngest at first calving. Straightbred heifers gestated 1.3 d longer and were 45 d older (P less than .05) at first calving than crossbred heifers. Dairy females had greater peak and total milk yield than beef females (P less than .01). Overall straightbred and crossbred means for peak milk yield and total milk yield did not differ significantly.