Effects of estradiol cypionate dosage and body condition on reproductive performance of Nellore cattle synchronized for timed-artificial insemination.

This experiment was designed to evaluate the effects of increasing doses of estradiol cypionate (ECP) and different body condition score (BCS) on reproductive performance of Bos indicus beef females assigned to a timed-artificial insemination (TAI) management. In this experiment, 1683 Bos indicus Nellore cows were blocked by parity and assigned to receive 1) an intravaginal P4 device (1.9 g of P4) and 2.0 mg of estradiol benzoate on day -11, 12.5 mg (i.m.) of dinoprost tromethamine, 300 IU (i.m.) of equine chorionic gonadotrophin, 0.6 mg (i.m.) of estradiol cypionate and CIDR withdrawal on day -2, followed by TAI on day 0 (n = 849; 0.6ECP) or 2) the same synchronization protocol with 1.0 mg of ECP on day -2 (n = 834; 1.0ECP). In both treatments, estrus expression was measured between days -2 and 0. Body condition score (BCS) was evaluated on days -11, 31, and 71 of the experiment and the BCS variation (Δ) was also determined between these timepoints. Transrectal ultrasonography was performed on days 31, 71, and 111 for pregnancy rate determination. All binary data were analyzed using cow as the experimental unit with GLIMMIX, whereas continuous variables were analyzed with the MIXED procedure of SAS. No treatment effects were observed on estrus expression rate. Treatment × BCS interactions were observed for pregnancy rates in all time points (days 31, 71, and 111), as 1.0ECP cows with a LOW BCS also had a greater P/AI than cows assigned to 0.6ECP. In summary, increasing the dose of ECP benefited the reproductive performance of Nellore beef cows with a reduced BCS (≤2.75), whereas no benefits were seen when the BCS was considered adequate (>2.75).

Reproductive programs for beef cattle: incorporating management and reproductive techniques for better fertility

This review summarizes strategies to increase overall pregnancy rates to TAI protocols, and potential areas for improvement in reproductive management of Nelore cows. Low BCS at calving and postpartum BCS loss negatively impacted percentage of pregnant females to TAI, with primiparous cows being the most sensitive to the effects of low BCS during the postpartum period. The current reproductive management recommended for replacement heifers (with TAI on day 0) consist of intravaginal progesterone device insertion from day -35 to -23, 0.6 mg i.m. injection of estradiol cypionate on day -23, insertion of another intravaginal progesterone device and 2.0 mg i.m. injection of estradiol benzoate on day -11, 12.5 mg i.m. injection of dinoprost tromethamine on day -4, intravaginal progesterone device removal and 0.6 mg i.m. injection of estradiol cypionate on day -2, and TAI on day 0. Supplementing corn for 41 days after the first TAI of the breeding season increased pregnancy to a second AI in primiparous cows, increased final proportion of pregnancy in primiparous cows, but decreased the final proportion of pregnancy in mature cows. In turn, supplementing melengestrol acetate or Ca salts of PUFA during the expected time of luteolysis was beneficial to pregnancy rates. Vaccinating cows against BoHV-1, BVDV, and Leptospira spp., particularly when both doses were administered before TAI, improved cow reproductive performance. Cow temperament has direct implications not only on reproductive efficiency of B. indicus females, but also on overall production efficiency in cow-calf system based on B. indicus cattle. Lastly, concentration of pregnancy-associated glycoproteins was driven by the ability of pregnancy maintenance and by sire used at TAI, whereas exploring this relationship might be interesting to improve sire fertility regarding late embryonic loss in Nelore females.(AU)

Reproductive programs for beef cattle: incorporating management and reproductive techniques for better fertility

This review summarizes strategies to increase overall pregnancy rates to TAI protocols, and potential areas for improvement in reproductive management of Nelore cows. Low BCS at calving and postpartum BCS loss negatively impacted percentage of pregnant females to TAI, with primiparous cows being the most sensitive to the effects of low BCS during the postpartum period. The current reproductive management recommended for replacement heifers (with TAI on day 0) consist of intravaginal progesterone device insertion from day -35 to -23, 0.6 mg i.m. injection of estradiol cypionate on day -23, insertion of another intravaginal progesterone device and 2.0 mg i.m. injection of estradiol benzoate on day -11, 12.5 mg i.m. injection of dinoprost tromethamine on day -4, intravaginal progesterone device removal and 0.6 mg i.m. injection of estradiol cypionate on day -2, and TAI on day 0. Supplementing corn for 41 days after the first TAI of the breeding season increased pregnancy to a second AI in primiparous cows, increased final proportion of pregnancy in primiparous cows, but decreased the final proportion of pregnancy in mature cows. In turn, supplementing melengestrol acetate or Ca salts of PUFA during the expected time of luteolysis was beneficial to pregnancy rates. Vaccinating cows against BoHV-1, BVDV, and Leptospira spp., particularly when both doses were administered before TAI, improved cow reproductive performance. Cow temperament has direct implications not only on reproductive efficiency of B. indicus females, but also on overall production efficiency in cow-calf system based on B. indicus cattle. Lastly, concentration of pregnancy-associated glycoproteins was driven by the ability of pregnancy maintenance and by sire used at TAI, whereas exploring this relationship might be interesting to improve sire fertility regarding late embryonic loss in Nelore females.

Características da carcaça e do corpo vazio de bovinos Charolês de diferentes categorias abatidos com similar grau de acabamento / Carcass characteristics and empty body of Charolais cattle of different categories slaughtered at similar degree of fatness

Avaliaram-se as características de carcaça e do corpo vazio de novilhos (NO), novilhas (NA) e vacas de descarte (VA) Charolês n= 9, 10 e 10, respectivamente, terminados em confinamento e abatidos com similar grau de acabamento. O peso de abate e o peso de corpo vazio (PCVZ) foram similares entre NO, 480,2 e 417,4kg, e VA, 516,2 e 405,8kg, e maiores do que os das NA, 368,3 e 306,1kg. O rendimento de carcaça quente diferiu entre as categorias, sendo 57,2, 53,3 e 50,5%, respectivamente, para NO, NA e VA. Com o rendimento de carcaça quente expresso em relação ao PCVZ, as diferenças entre categorias diminuíram, sendo significativas apenas entre NO e NA. O conteúdo do trato digestivo das VA foi 34 e 45% maior que o dos NO e NA, respectivamente, sendo correlacionado (P<0,05) com peso de abate (r=0,66) e rendimento de carcaça quente (r=-0,41). O peso de carcaça quente foi similar entre NO, 274,9kg, e VA, 260,8kg, e maior que o NA, 196,4kg. O comprimento de carcaça foi maior nas VA, intermediário nos NO e menor nas NA. A área do músculo Longissimus dorsi foi menor nas NA. Novilhos apresentaram melhor conformação de carcaça que as fêmeas, as quais não diferiram entre si.(AU)

The carcass characteristics and empty body of Charolais steers n=9, cull heifers n= 10, and cull cows n=10, feedlot finished with similar subcutaneous fat thickness were evaluated. The slaughter weight and empty body weight (EBW) were similar between steers (480.2 and 417.4kg) and cows (516.2 and 405.8kg), which were higher than for heifers (368.3 and 306.1kg). Hot carcass dressing was significantly different among categories, being 57.2, 53.3 and 50.5%, respectively, for steers, heifers and cows. When carcass dressing was expressed in relation to EBW the differences became smaller among categories, being significant only between steers and heifers. The digestive tract content of cows was 34 and 45% higher than for steers and heifers, respectively, being correlated (P<0.05) with slaughter weight (r=0.66) and hot carcass dressing (r=-0.41). Hot carcass weight was similar for steers (274.9kg) and cows (260.8kg), both superior to heifers (196.4kg). Carcass length was higher for cows, intermediate for steers and lower for heifers. The Longissimus dorsi area was smaller for heifers. Steers showed better carcass conformation score than females, which did not differ between themselves.(AU)

Características da carcaça e do corpo vazio de bovinos Charolês de diferentes categorias abatidos com similar grau de acabamento / Carcass characteristics and empty body of Charolais cattle of different categories slaughtered at similar degree of fatness

Avaliaram-se as características de carcaça e do corpo vazio de novilhos (NO), novilhas (NA) e vacas de descarte (VA) Charolês n= 9, 10 e 10, respectivamente, terminados em confinamento e abatidos com similar grau de acabamento. O peso de abate e o peso de corpo vazio (PCVZ) foram similares entre NO, 480,2 e 417,4kg, e VA, 516,2 e 405,8kg, e maiores do que os das NA, 368,3 e 306,1kg. O rendimento de carcaça quente diferiu entre as categorias, sendo 57,2, 53,3 e 50,5%, respectivamente, para NO, NA e VA. Com o rendimento de carcaça quente expresso em relação ao PCVZ, as diferenças entre categorias diminuíram, sendo significativas apenas entre NO e NA. O conteúdo do trato digestivo das VA foi 34 e 45% maior que o dos NO e NA, respectivamente, sendo correlacionado (P<0,05) com peso de abate (r=0,66) e rendimento de carcaça quente (r=-0,41). O peso de carcaça quente foi similar entre NO, 274,9kg, e VA, 260,8kg, e maior que o NA, 196,4kg. O comprimento de carcaça foi maior nas VA, intermediário nos NO e menor nas NA. A área do músculo Longissimus dorsi foi menor nas NA. Novilhos apresentaram melhor conformação de carcaça que as fêmeas, as quais não diferiram entre si.

The carcass characteristics and empty body of Charolais steers n=9, cull heifers n= 10, and cull cows n=10, feedlot finished with similar subcutaneous fat thickness were evaluated. The slaughter weight and empty body weight (EBW) were similar between steers (480.2 and 417.4kg) and cows (516.2 and 405.8kg), which were higher than for heifers (368.3 and 306.1kg). Hot carcass dressing was significantly different among categories, being 57.2, 53.3 and 50.5%, respectively, for steers, heifers and cows. When carcass dressing was expressed in relation to EBW the differences became smaller among categories, being significant only between steers and heifers. The digestive tract content of cows was 34 and 45% higher than for steers and heifers, respectively, being correlated (P<0.05) with slaughter weight (r=0.66) and hot carcass dressing (r=-0.41). Hot carcass weight was similar for steers (274.9kg) and cows (260.8kg), both superior to heifers (196.4kg). Carcass length was higher for cows, intermediate for steers and lower for heifers. The Longissimus dorsi area was smaller for heifers. Steers showed better carcass conformation score than females, which did not differ between themselves.