Interactive response of the horn fly (Diptera: Muscidae) and selected breeds of beef cattle

Statistically significant differences were observed in the population density of the horn fly, Haematobia irritans irritans (L.), on different breeds of beef cattle. The European breed Chianina had a population density of horn flies generally less than or equal to 50% than that of the British cattle breeds (Angus, Hereford, Polled Hereford, and Red Poll) and another European breed (Charolais). Generally, no significant difference existed among numbers of horn flies on Hereford, Polled Hereford, and Red Poll cows in 1988 or among Angus, Hereford, Polled Hereford, and Red Poll cows in 1989. Factors other than color appeared to be involved in the selective process between the horn fly and its host. Population densities on two white European breeds (Charolais and Chianina) were significantly different on all weekly intervals except for 4 wk in both 1988 and 1989. No significant difference existed among Charolais and British breeds except during 4 wk in 1988 and 3 wk in 1989. When weaning weights of all calves were adjusted for the effects of age to 205 d, sex of calf, and age of dam, the indirect effect of the horn fly on weaning weight showed a significant linear regression. Each 100 flies per cow caused a reduction of 8.1 kg in calf weaning weight. Cows within each breed with low numbers of horn flies weaned significantly heavier calves than cows with higher numbers of horn flies.     

Effect of rumen-protected methionine supplementation to beef cows during the periconception period on performance of cows,calves, and subsequent offspring

Maternal nutrition affects the development of the fetus and postnatal performance of the calf. Methionine may play a critical role in developmental programming and is likely deficient in beef cows fed low-quality forage. The objective of this study was to determine the effect of metabolizable methionine supply to lactating beef cows during the periconception period on performance of cows, calves, and subsequent offspring. This project involved two consecutive production cycles commencing at calving in which dietary treatments were fed to cows during the periconception period along with measurements on cows and initial calves in Production Cycle 1, and measurements on subsequent calves in Production Cycle 2. Brangus-Angus crossbred lactating beef cows (N = 108; age = 6.4 (2.8) year) were stratified by previous calving date and assigned to one of three supplements: (1) control, molasses plus urea at 2.72 kg/day as fed, (2) fishmeal, 2.27 kg/day molasses plus urea plus 0.33 kg/day as fed of fishmeal, and (3) methionine, 2.72 kg/day of molasses plus urea plus 9.5 g/day of 2-hydroxy-4-(methylthio)-butanoic acid. Cows were fed supplements and low-quality limpograss (Hemarthria altissima) hay while grazing dormant bahiagrass (Paspalum notatum Flüggé) pastures during the 115-day periconception period from December 2014 to April 2015 in Production Cycle 1 only. Body weight change and milk yield of cows were measured during the periconception period in Production Cycle 1. Body weight of calves was measured at birth and weaning in both production cycles. Following weaning in Production Cycle 2, eight subsequent steer calves per treatment were individually housed for a 42-day metabolism experiment. Treatment did not affect (P > 0.10) BW change of cows, but cows fed methionine tended (P = 0.09) to produce more energy-corrected milk than control and fishmeal. Treatment did not affect (P > 0.10) 205-day adjusted weaning weight of calves in either production cycle. During the metabolism experiment, subsequent calves from dams fed fishmeal and methionine gained faster (P < 0.05) and had greater (P < 0.05) gain:feed than control calves. Methionine calves tended (P = 0.06) to have greater apparent total tract NDF and ADF digestibility and lesser (P < 0.05) blood glucose concentration than control and fishmeal calves. These data indicate that maternal methionine supply during the periconception period plays an important role in programming future performance of the offspring.     

Applications of sexed semen in cattle production

Sexed semen will contribute to increased profitability of dairy and beef cattle production in a variety of ways. It could be used to produce offspring of the desired sex from a particular mating to take advantage of differences in value of males and females for specific marketing purposes. Commercial dairy farmers, those who produce and market milk, could use sexed semen to produce replacement daughters from genetically superior cows and beef crossbred sons from the remainder of their cow population. To increase the rate of response to selection, seedstock dairy cattle breeders could produce bulls for progeny testing from a smaller number of elite dams by using sexed semen to ensure that all of them produced a son. Using sexed semen could then reduce the cost of progeny testing those bulls, because fewer matings would be necessary to produce any required number of daughters. Commercial beef cattle farmers, producing animals for eventual slaughter, could use sexed semen to capitalize on the higher value of male than female offspring for meat production. They could also use sexed semen to produce specialized, genetically superior replacement heifers from as small a proportion of the herd as possible. This would allow the remainder of the herd to produce male calves from bulls or breeds with superior genetic merit for growth, feed conversion efficiency, and carcass merit. Single-sex, bred-heifer systems, in which each female is sold for slaughter soon after weaning her replacement daughter, would be possible with the use of X-chromosome-sorted semen. Use of sexed semen would make terminal crossbreeding systems more efficient and sustainable in beef cattle. Fewer females would be required to produce specialized maternal crossbred daughters, and more could be devoted to producing highly efficient, terminal crossbred sons.     

Influence of 48 hour calf separation on milk production and calf growth in range cows

Hereford cows and their calves were either left together or separated for a 48-hr period between 50 and 80 days postpartum. Milk production and calf weights were determined 1 and 2 weeks prior to and 1 and 3 weeks after calf separation. Daily milk production of separated cows (5.6+/-.1 kg) was not different from that of control cows (5.3+/-.1 kg) at any sampling period. Similarly, calf growth was not affected (P > .10) by separation; both groups of calves gained .64 kg/day. Average 205-day adjusted weaning weights were also similar, for the control (173.5+/-4.6 kg) and separated calves (181.8+/-4.6 kg). These results indicate that 48-hr calf separation could be used in a treatment regime to decrease the postpartum anestrous interval in range cattle without detrimental effects on milk production, calf growth or 205-day adjusted weaning weight.     

Effect of dam factors on milk intake and performance of Belgian Blue suckling calves

Milk intake data were collected at 4-week intervals from Belgian Blue double-muscled (BBDM) suckling calves up to 16 weeks after birth. Dams were fed at 100%, 90%, 80% or 70% of their energy requirements during a 140-day indoor period from the beginning of December to the end of April (restriction period). Afterwards, cows were turned out on pasture (re-alimentation period). Mean calving date was 3 June, but parturitions were spread over the year. A total of 521 individual milk intake (IMI) and 120 average daily milk intake (AMI, mean of IMI) records were collected. IMI amounted to 7.0 ± 2.2 kg/day and was not affected by energy level during the indoor period. It was highest in May and June. Calves born out of multiparous cows consumed more milk than those born out of primiparous cows (7.4 v. 6.2 kg per day; P = 0.001), while intake tended to be higher in female than in male calves (7.2 v. 6.8 kg per day; P = 0.044). Dam age at calving, parity, post partum weight and body condition were only weakly correlated with AMI (r 0.4). AMI was correlated with pre-weaning live-weight gain (r = 0.807) and weaning weight (r = 0.783), with a slightly higher correlation for male than for female calves. Daily live-weight gain during the suckling period was increased by 79 g per extra kg daily milk intake on average, and by 86 and 74 g, respectively, for male and female calves. Calf solid feed intake was low, even when milk intake was low. In terms of net energy intake, milk was only substituted for solid feed by 29%. It can be concluded from the calf intake that milk production in BBDM cows is comparable with that of cows from other beef breeds, but its variation is considerable, complicating an accurate estimation.     

Minimizing cows’ stress when calves were early weaned using the two-step method with nose flaps

Early weaning may be used in beef cattle production to improve reproduction rates in range conditions. However, weaning causes a stress response in cows, which may be especially strong in early weaning management, as the bond between the cow and the calf is still strong. We hypothesized that weaning calves in two steps, with the aid of anti-sucking devices (nose flaps) would reduce the behavioural stress response in the cows separated from their calves 2 months after parturition. We compared the behaviour frequency and weight change in cows that were weaned abruptly, by separation of the calf on day 0 of the study, or in two steps, consisting of the use of anti-sucking nose flaps for 5 days before permanent separation; a third group was not weaned to serve as control. Thirty-six crossbred multiparous Aberdeen Angus×Hereford cows and their calves (n=12/treatment) were managed in three paddocks with similar pasture availability, with four dyads from each treatment per paddock. Cows’ behaviour was observed by direct visual instantaneous sampling, at 10 min intervals from days −3 to 11. Weaning the calves in two steps clearly attenuated the behavioural stress response observed in abruptly weaned cows, which included reductions in grazing and lying, and increases in pacing, walking and vocalizing. Our results corroborate those previously shown for cows nursing older calves, and indicate that step weaning can reduce the behavioural stress response of cows at weaning, even when the calf is weaned shortly after birth, when the bond between the cow and calf is still very strong.     

Behaviour of Zebu and crossbed cows in restricted suckling groups

The aim of this study was to investigate whether Zebu (Bos indicus) and crossbred (Bos indicusxBos taurus) cows differ in maternal related behaviour during restricted group suckling. The behaviours of 20 Zebu and 16 crossbred cows were recorded during two 30min sessions each day after milking when their calves were present for suckling, for a time period of 2 weeks per month for 6 months postpartum. The main activity in both breeds during the 0.5h observation sessions was suckling. However, the two breeds differed significantly in several behavioural aspects. The Zebu cows had longer total duration of suckling than the crossbred cows, per 30min session, 11.8 and 9.4min, respectively. The separate suckling bouts were longer in the Zebu cows (2.8min in Zebu and 2.3min in crossbred) and this breed also had more suckling bouts than the crossbred per session, 3.8 and 3.2, respectively. Zebu cows stayed in close contact with their calves for longer time and directed more agonistic actions against alien calves and cows than the crossbred cows.     

Short estrous cycles and associated serum progesterone levels in beef cows

Short estrous cycles in beef cows were investigated in two experiments. In trial 1, breeding dates from 2,854 fall-calving Angus cows were used to determine the incidence of short estrous cycles. Of 198 cycles of less than 17 days, 170 were between the first and second detected estrus. Estrous cycles of 7 to 10 days occurred more frequently (P<.005) than other short estrous cycles. Eight-day estrous cycles were most frequent. In the second experiment, calves were weaned from 25 of 33 anestrous spring-calving, crossbred Simmental cows. Compared to herdmates still nursing calves, an increased percentage of cows which had calves weaned were observed in estrus within 10 and 25 days after the date of weaning (P<.005) and a higher percentage had 7- to 10-day estrous cycles. Cows that were observed in estrus within 10 days after weaning were inseminated with Angus semen at their first estrus and with Simmental semen at their second estrus. No cows conceived on the first estrus of 7- to 10-day estrous cycles; 61.5% conceived on the second estrus. Serum progesterone was higher (P<.01) before the second estrus than the first.     

Testicular size at weaning in tropically-adapted beef bulls as influenced by breed of sire and dam

This study was conducted to evaluate testicular size at weaning for bulls representing diverse tropically-adapted genotypes. Calves from 2 locations were weighed and castrated at weaning. In one herd, calves were born to Brahman dams and Angus, Tuli, and Brahman sires. Body weights and paired testes weights were heavier (P < 0.01) for Angus x Brahman (AB) genotype than for Tuli x Brahman (TB) and purebred Brahman (BB) genotype calves. The testes:body weight ratio was greater (P < 0.01) for AB than for TB and BB calves. In a second herd, calves were born to Angus cows and Brahman, Tuli, and Senepol sires. Means were similar between Brahman- (BA), Tuli-(TA), and Senepol-sired (SA) calves for body weight and testes:body weight ratio. Paired testes weight was heavier (P < 0.05) for SA than BA calves. Across locations, paired testes weights were heavier (P < 0.01) for TA than TB calves but their body weights were similar. Within-herd deviations were greater (P < 0.01) for AB than BA calves for paired testes weight and testes:body weight ratio. The correlation between the proportion of Bos indicus genetic contribution and testes:body weight ratio was significantly negative. Tropically-adapted calves differed in testicular size at weaning due to breed of sire and dam effects.     

Factors associated with selling price of cattle at livestock marts

The objective of this study was to determine the factors associated with selling price of animals at livestock marts around Ireland. Data consisted of four distinct maturity categories: calves (2 to 84 days of age, n = 53 838); weanlings (6 to 12 months of age, n = 19 972); post-weanlings (12 to 36 months of age, n = 93 081) and cows (>30 months to 12 years of age, n = 94 839); sold through livestock marts between 2000 and 2008. Factors associated with animal price were determined within each maturity category separately using mixed models; random effects were mart, date of sale nested within mart, and herd of origin nested within year of sale. Mean selling price was €157, €580, €655 and €592 for calves, weanlings, post-weanlings and cows, respectively. The greatest prices were paid for singleton crossbred male calves, weanlings and post-weanlings from older dams. With the exception of the Aberdeen Angus, beef breeds and their crosses consistently received higher prices than their dairy counterparts across all four maturity categories; increased proportion of Belgian Blue and Charolais was associated with greater prices compared with other beef breeds. When live-weight was included in the multiple regression models the association between price and all factors regressed toward zero but most factors remained associated with price. The highest price was recorded in the spring months for calves, post-weanlings and cows, and in the autumn months for weanlings. Results from this study may be used to help farmers make more informed management decisions, as well as provide information for bio-economic models for evaluating alternative production systems or estimating economic values.     

Evaluation of production efficiencies at pasture of lactating suckler cows of diverse genetic merit and replacement strategy

Feed costs account for the largest proportion of direct cost within suckler beef production systems. By identifying the cow type with enhanced capability of converting grazed herbage to beef output across lactations, suckler cow systems would become more efficient and sustainable. The objective of this study was to estimate grass DM intake (GDMI) and production efficiency among lactating suckler cows of diverse genetic merit for the national Irish maternal index (Replacement Index) which includes cow efficiency components such as milk yield and feed intake. Data from 131 cows of diverse genetic merit within the Replacement Index, across two different replacement strategies (suckler or dairy sourced), were available over two grazing seasons. Milk yield, GDMI, cow live weight (BW) and body condition score (BCS) were recorded during early, mid and late-lactation, with subsequent measures of production efficiency extrapolated. Genetic merit had no significant effect on any variables investigated, with the exception of low genetic merit (LOW) cows being 22 kg heavier in BW than high genetic merit (HIGH) cows (P < 0.05). Beef cows were 55 kg heavier in BW (P < 0.001), had a 0.31 greater BCS (P < 0.05) and 0.30 Unité Fourragère Lait (UFL) greater energy requirement for maintenance compared to dairy sourced beef × dairy crossbred (BDX) cows (P < 0.001). The BDX had 0.8 kg greater GDMI, produced 1.8 kg more milk (P < 0.001), had a 0.8 UFL greater energy requirement for lactation and produced weanlings that were 17 kg heavier in BW than beef cows (P < 0.05). Subsequent efficiency variables of milk per 100 kg BW (P < 0.001), milk per kg GDMI (P < 0.001) and GDMI per 100 kg BW (P < 0.001) were more favourable for BDX. The correlations examined showed GDMI had moderate positive correlations (P < 0.001) with intake per 100 kg BW, net energy intake per kg milk yield, RFI and intake per 100 kg calf weaning weight but was weakly negatively correlated to milk yield per kg GDMI (P < 0.001). No difference was observed across genetic merit for beef cows for any of the traits investigated. Results from the current study showed that, while contrasting replacement strategies had an effect on GDMI and production efficiency, no main effect was observed on cows diverse in genetic merit for Replacement Index. Nonetheless, utilising genetic indexes in the suckler herd is an important resource for selecting breeding females for the national herd and phenotypic performance generated from this study can be included in future genetic evaluations to improve reliability of genetic values.     

Influence of Restricted Suckling and Level of Feed Supplementation on Postpartum Reproductive Performance of Zebu and Crossbred Cattle in the Semi-Arid Tropics

This study was carried out in central Tanzania on a group of 45 Zebu and 37 crossbred cows which were 4 to 10 years old. At calving time, the animals were allocated to one of the 4 treatment groups. In addition to free access to grazing for all cows in the study, in group H: AR (n = 18), cows were fed a high level of concentrate supplementation (4kg/day) and calves were artificially reared; in group H:RS (n = 24), cows were fed a high level of concentrate supplementation (4kg/day) and calves were only allowed restricted suckling up until the weaning age of 6 months. In group L:AR (n = 23) cows were fed a low level of concentrate supplementation (2kg/day) and calves were artificially reared; and in group L:RS (n = 17) cows were fed a low level of concentrate supplementation (2kg/day) and calves were only allowed restricted suckling up until the weaning age of 6 months. Milk progesterone was used as a means of determining the postpartum resumption interval (PRI) and the interval from parturition to conception (PCI). The overall PRI was 47.4 ± 0.4 days and was significantly affected by breed but not by calving season, with crossbred cows exhibiting a shorter PRI than Zebu cows. The effect of the treatments was significant, with cows in the group H:AR displaying a significantly shorter PRI than those in the other groups, while cows in group L:RS showed a significantly longer PRI than those in the other groups. The overall PCI was 149.5 ±3.7 days, and was not significantly affected by breed or calving season. The effect of the treatments was significant, with cows in the group H:AR having a significantly shorter PCI than cows in the other groups, while cows in group L:RS showed a significantly longer PCI than those in the other groups. Crossbred cows had higher live weights at calving (299.4 kg) than Zebu cows (272.6 kg), while all cows gained weight during the first 3 months after calving. The treatments had a significant effect on weight gain, with cows in the group H:AR gaining significantly more weight than those in the other groups. Cows which had high live weights at calving exhibited significantly shorter PRI and PCI than the lighter cows. Animals which had gained more than 5 kg during the first month after calving, or which had gained more than 8 kg during the first 3 months after calving, showed significantly shorter PRI and PCI than cows which had gained less weight. The results show that the calf rearing system and the level of feed supplementation interact with each other and can influence the postpartum anoestrous period in Zebu and Zebu crossbred cattle. Increasing the level of nutrition in restricted suckling cows tended to improve the postpartum anoestrous period, but the positive effects of supplementation could not completely compensate for the negative effects of suckling.     

Post-weaning feed efficiency decreased in progeny of higher milk yielding beef cows

Current trends in the beef industry focus on selecting production traits with the purpose of maximizing calf weaning weight; however, such traits may ultimately decrease overall post-weaning productivity. Therefore, the objective of this study was to evaluate the effects of actual milk yield in mature beef cows on their offspring’s dry matter intake (DMI), BW, average daily gain, feed conversion ratio (FCR) and residual feed intake (RFI) during a ~75-day backgrounding feeding trial. A period of 24-h milk production was measured with a modified weigh-suckle-weigh technique using a milking machine. After milking, cows were retrospectively classified as one of three milk yield groups: Lower (6.57±1.21 kg), Moderate (9.02±0.60 kg) or Higher (11.97±1.46 kg). Calves from Moderate and Higher milk yielding dams had greater (P<0.01) BW from day 0 until day 75 at the end of the backgrounding feeding phase; however, day 75 BW were not different (P=0.36) between Lower and Moderate calves. Body weight gain was greater (P=0.05) for Lower and Moderate calves from the day 0 BW to day 35 BW compared with Higher calves. Overall DMI was lower (P=0.03) in offspring from Lower and Moderate cows compared with their Higher milking counterparts. With the decreased DMI, FCR was lower (P=0.03) from day 0 to day 35 in calves from Lower and Moderate milk yielding dams. In addition, overall FCR was lower (P=0.02) in calves from Lower and Moderate milk yielding dams compared with calves from Higher milk yielding dams. However, calving of Lower milk yielding dams had an increased (P=0.04) efficiency from a negative RFI value compared with calves from Moderate and Higher milking dams. Results from this study suggest that increased milk production in beef cows decreases feed efficiency during a 75-day post-weaning, backgrounding period of progeny.     

Does increasing milk yield per cow reduce greenhouse gas emissions? A system approach

Milk yield per cow has continuously increased in many countries over the last few decades. In addition to potential economic advantages, this is often considered an important strategy to decrease greenhouse gas (GHG) emissions per kg of milk produced. However, it should be considered that milk and beef production systems are closely interlinked, as fattening of surplus calves from dairy farming and culled dairy cows play an important role in beef production in many countries. The main objective of this study was to quantify the effect of increasing milk yield per cow on GHG emissions and on other side effects. Two scenarios were modelled: constant milk production at the farm level and decreasing beef production (as co-product; Scenario 1); and both milk and beef production kept constant by compensating the decline in beef production with beef from suckler cow production (Scenario 2). Model calculations considered two types of production unit (PU): dairy cow PU and suckler cow PU. A dairy cow PU comprises not only milk output from the dairy cow, but also beef output from culled cows and the fattening system for surplus calves. The modelled dairy cow PU differed in milk yield per cow per year (6000, 8000 and 10 000 kg) and breed. Scenario 1 resulted in lower GHG emissions with increasing milk yield per cow. However, when milk and beef outputs were kept constant (Scenario 2), GHG emissions remained approximately constant with increasing milk yield from 6000 to 8000 kg/cow per year, whereas further increases in milk yield (10 000 kg milk/cow per year) resulted in slightly higher (8%) total GHG emissions. Within Scenario 2, two different allocation methods to handle co-products (surplus calves and beef from culled cows) from dairy cow production were evaluated. Results showed that using the 'economic allocation method', GHG emissions per kg milk decreased with increasing milk yield per cow per year, from 1.06 kg CO2 equivalents (CO2eq) to 0.89 kg CO2eq for the 6000 and 10 000 kg yielding dairy cow, respectively. However, emissions per kg of beef increased from 10.75 kg CO2eq to 16.24 kg CO2eq due to the inclusion of suckler cows. This study shows that the environmental impact (GHG emissions) of increasing milk yield per cow in dairy farming differs, depending upon the considered system boundaries, handling and value of co-products and the assumed ratio of milk to beef demand to be satisfied.     

Polymorphisms of <Emphasis Type="Italic">STAT5A</Emphasis> gene and their association with milk production traits in Holstein cows

The STAT5A gene was studied as a candidate gene for five milk production traits (milk yield at 305 days, protein percentage, fat percentage, lactose percentage and dry matter percentage) in Holstein cows. According to the sequence of bovine STAT5A gene, two pairs of primers (P1 and P2) were designed to detect polymorphisms of STAT5A gene in 401 Holstein cows by PCR-RFLP and PCR-SSCP. The results showed that the products amplified by primers P1 and P2 displayed polymorphisms. For P1, three genotypes (AA, AG, and GG) were detected, and the frequency of AA/AG/GG was 0.252/0.486/0.262, respectively. Sequence analysis revealed a single nucleotide substitution A–G at 14217 bp (GenBank NC_007317) of bovine STAT5A gene while compared GG genotype with AA genotype. The differences of the least squares means for the four milk production traits (milk yield at 305 days, fat percentage, lactose percentage and dry matter percentage) between AA, AG and GG were not significant (P > 0.05). Least squares mean of protein percentage for AG or GG was significantly higher than that for AA (P < 0.05); the difference of the least squares mean for protein percentage was not significant between AG and GG (P > 0.05). For P2, three genotypes (CC, CT, and TT) were detected in Holstein cows, and the frequency of CC/CT/TT was 0.751/0.234/0.015, respectively. Sequencing revealed an insertion CCT at 17266 (NC_007317) of bovine STAT5A gene while compared CC genotype with TT genotype. The differences of the least squares means for the three milk production traits (protein percentage, lactose percentage and dry matter percentage) between CC, CT and TT were not significant (P > 0.05). Least squares mean of milk yield at 305 days for TT or CT was significantly higher than that for CC (P < 0.05); the difference of the least squares mean for milk yield at 305 days was not significant between TT and CT (P > 0.05). Least squares mean of fat percentage for CC or CT was significantly higher than that for TT (P < 0.05); the difference of the least squares mean for fat percentage was not significant between CC and CT (P > 0.05). The results preliminarily indicated that allele G of A14217G polymorphic site of STAT5A gene is a potential DNA marker for improving protein percentage in dairy cattle, 17266indelCCT polymorphic site of STAT5A gene is a potential DNA marker for improving milk yield at 305 days and fat percentage in dairy cattle.     

Effect of cow replacement strategy on cow and calf performance in the beef herd

Two contrasting replacement strategies are used by Irish beef farmers to select replacement females – animals sourced from within the suckler beef herd and sourced from the dairy herd. The objective of this study was to investigate the effect of replacement strategy (i.e. beef v. beef×dairy (BDX)) on cow and calf performance using data from the national beef database across a range of beef and dairy breeds. The association between replacement strategy and calving difficulty score, calving interval, weaning weight, weaning price and all carcass traits was investigated using a mixed model. The effect of replacement strategy on cow survival, calving dystocia and calf perinatal mortality was quantified using logistic regression. Beef cows were older (10.92 days; P<0.001) at their first calving, but were 1.15 times (P<0.01) more likely to survive to a subsequent lactation compared with BDX cows. Calving interval was 1.53 days shorter (P<0.001) for BDX compared with beef cows. Greater calving difficulty and calving dystocia was associated with beef cows (P<0.001) relative to BDX. However, BDX were 1.36 times (P<0.001) more likely to have a dead calf at birth relative to beef cows. Calves weaned from BDX were heavier (18.49 kg; P<0.001) at weaning, reached slaughter 12.8 days earlier (P<0.001), had 7.99 kg heavier carcass (P<0.001) and a greater fat score (P<0.001) compared with the progeny of beef cows. Beef cow progeny had a superior conformation score (0.5; P<0.001) and achieved a greater price per kilogram (P<0.001) compared with progeny from BDX. Beef cull cows had a heavier carcass (5.58 kg), superior carcass conformation, greater carcass price per kilogram and greater overall carcass value (P<0.001) than BDX. Results from this study show that replacement strategy is of fundamental importance depending on the type of system implemented by farmers and consideration must be given to the traits of importance within the context of the individual production system.     

Review: passive immunity in beef-suckler calves

Colostrum-derived passive immunity is central to the health, performance and welfare of neonatal beef-suckler calves, and economics of beef-farming enterprises. Compared to dairy calves, mainly Holstein-Friesian, there is much less research carried out on passive immunity and associated factors in beef calves. Thus, this review aimed to summarise and interpret published information and highlight areas requiring further research. The transfer of immunoglobulin G1 (IgG1) from blood to mammary secretions is greater for beef × dairy cows compared to most beef breed types. Considerable between-animal variance is evident in first-milking colostrum yield and immunoglobulin concentration of beef-suckler cow breed types. First-milking colostrum immunoglobulin concentrations are similar for within-quarter fractions and for the front and rear quarters of the udder. First-milking colostrum yield is higher for beef × dairy cows than beef × beef and purebred beef breeds, and higher for multiparous than primiparous cows, but generally colostrum immunoglobulin concentration is relatively similar for each of the respective categories. Consequently, colostrum immunoglobulin mass (volume × concentration) production in beef cows seems to be primarily limited by colostrum volume. The effect of maternal nutrition during late gestation on colostrum yield is not well documented; however, most studies provide evidence that colostrum immunoglobulin concentration is not adversely affected by under-nutrition. Factors that impinge upon the duration between birth and first suckling, including dam parity, udder and teat anatomy and especially dystocia, negatively impact on calf passive immunity. Colostrum immunoglobulin mass ingested relative to birth weight post-parturition is the most important variable determining calf passive immunity. Research indicates that feeding the beef calf a colostrum volume equivalent to 5% of birth weight shortly after parturition, with subsequent suckling of the dam (or a second feed) 6 to 8 h later, ensures adequate passive immunity, equivalent to a well-managed suckling situation. Within beef-suckler cow genotypes, calf passive immunity is similar for many common beef breeds, but is generally higher for calves from beef × dairy cows. Compared to older cows, calves from younger cows, especially primiparous animals, have lower serum immunoglobulin concentrations. Most studies have shown no adverse impact of maternal dietary restriction on calf passive immunity. The prevalence of failure of passive transfer (FPT) in beef calves varies considerably across studies depending on the test used, and what cut-off value is assumed or how it is classified. The accuracy and precision of methodologies used to determine immunoglobulin concentrations is concerning; caution is required in interpreting laboratory results regarding defining colostrum ‘quality’ and calf passive immune ‘status’. Further research is warranted on colostrum-related factors limiting passive immunity of beef calves, and on the validation of laboratory test cut-off points for determining FPT, based on their relationships with key health and performance measures.     

Influence of exogenous steroids, nutrition and calf removal on reproductive performance of anestrous beef cows

Methods for inducing a fertile estrus in anestrous beef cows suckling calves were explored in three studies. Trial 1 . Eighty-two primiparous and pluriparous Brahman-Hereford crossbred and Angus cows suckling calves were divided into four groups: 1) good body condition, high level of nutrition (GH); 2) good body condition, low level of nutrition (GL); 3) poor body condition, high level of nutrition (PH); 4) poor body condition, low level of nutrition (PL). All cows received the Shang Treatment (S). Following treatment, more cows (P<0.05) ovulated in the GH group (95%) than either the GL (61%), PH (58%), or PL (53%) group. Pregnancy rates were low and were not different between groups following the insemination taking place 54 hours after implant removal or after cows had been bred for 21 days. Trial 2 . One hundred fourteen two-year-old Santa Gertrudis-Hereford crossbred cows in poor body condition were divided into four groups. Forty-nine cows received S treatment and 65 cows served as controls (C) with approximately half of each group fed a high (H) or a medium (M) level of nutrition (SH, SM, CH, CM). One cow in the SH group ovulated and was pregnant 21 days after breeding. The remaining cows failed to exhibit estrus, ovulate or become pregnant. Trial 3 . Cows used in this trial were those from Trial 2 which did not exhibit estrus nor had a palpable corpus luteum present 21 days after implant removal. Cows were divided into 1) control (C), 2) wean (W), 3) wean + Syncro-Mate-B (W+SMB) and 4) Syncro-Mate-B + wean (SMB+W). The percentage of cows ovulating by 2 and 40 days after the start of breeding was similar (P>0.05) in the W, W+SMB, and SMB+W groups but all were greater (P<0.05) than the percentage of cows ovulating in the C groups. Pregnancy rates of cows in the W+SMB and SMB+W groups were higher (P<0.05) than pregnancy rates of cows in the W and C groups by two days after the start of breeding. Pregnancy rates 40 days after the start of breeding were higher (P<0.05) for cows in the W, W+SMB) and SMB+W groups than for cows in the C group.     

Association between leptin single nucleotide polymorphism and reproductive performance of lactating Holstein cows

The objectives of the current study were to evaluate the associations among reproductive performance of Holstein cows, single nucleotide polymorphism (SNP) in the R4C locus of the Exon-2 region of the leptin gene and health disorders. Lactating dairy cows (n=814) had their DNA sequenced at the Exon-2 region of the leptin gene to determine the presence of SNP in the R4C locus. Cows had the stage of estrous cycle synchronized with two injections of PGF(2α) 14d apart, with or without a progesterone insert. After the second PGF(2α), cows were either inseminated on detected estrus and, if not inseminated within 13d, cows were submitted to a timed artificial insemination (AI) protocol 13d after the second PGF(2α). Blood was sampled at 35±3, 49±3, and 62±3d in milk (DIM) and cows with progesterone <1.0ng/mL in the first two samples were considered to be anovular, whereas those with at least one of the first two samples with progesterone ≥1.0ng/mL were considered to have initiated estrous cyclicity. Anovular cows with progesterone ≥1.0ng/mL at 62±3DIM were considered to have resumed estrous cyclicity. Pregnancy was diagnosed at 31 and 60d after first postpartum AI and at 42d after subsequent inseminations. Resulting genotypes were CC (34.6%), CT (48.2%), and TT (17.2%). Leptin genotype was associated (P=0.03) with increased prevalence of estrous cyclic cows at 49±3DIM, as TT cows were and tended to be less likely to be estrous cyclic than CC and CT cows, respectively. Other measures of reproductive performance in the first 305DIM were not associated with leptin genotype. Cows diagnosed with at least one postparturient disease were less likely to become pregnant after first (P<0.01) and second (P=0.02) AI and to be pregnant at 305DIM (P<0.01). Furthermore, cows diagnosed with a disease event had a 36% reduction (P<0.001) in the rate of pregnancy, which extended the median interval to pregnancy by 60d. Estrous cyclic cows had a 35% increased rate of pregnancy, which reduced the interval to pregnancy by 34d. Cows homozygous for the T allele were less likely to be cyclic early postpartum, but leptin genotype was not associated with other reproductive responses when cows were subjected to a controlled breeding program.     

The effects of twinning on mother—Offspring behavior in range beef cattle

Methods to increase the productivity of beef cattle include induced twinning and multiple fostering of calves on nurse cows, but little is known about the capacity of cows to rear more than one calf in a rangeland environment.Eight single and 14 twin calves and their mothers were studied in a 30.4-ha enclosure in a California rangeland environment from 2 to 20 weeks following parturition. Data were obtained on ingestive, grooming, agonistic, play and sexual behaviors, as well as spatial proximity of calves to mothers and peers.Initially, twins spent more time suckling their mothers than did single calves (presumably due to insufficient milk intake), but later adapted by utilizing natural forage and obtaining milk from alien cows. By 15–20 weeks of age, twins were suckling their dams for less than one-quarter of the time spent at 3–6 weeks, whereas the suckling time of single calves did not decline. Thus, twins may experience a natural early weaning from mother's milk.The hypothesis that mother—Offspring bonds are weaker with twins than with singles was supported by the fact that mothers bearing twins groomed their offspring less than mothers with singles, and twins were normally found at greater distances from their mothers than singles.Most long-distance cow—Calf separations resulted from the cow moving to feed or to obtain water. Reunion of mother and young depended on auditory communication; the calf normally traversed most of the intervening distance.