Abstract Reproductive failure and pregnancy loss in cattle are some of the largest economic burdens to cattle producers and one of most perplexing factors influencing management decisions. Pregnancy loss may occur at any point during gestation with the largest percentage of loss occurring in the first 30 days and, subsequently, decreasing as the pregnancy progresses. Losses may be attributed to numerous factors, predisposed issues or environmental conditions such as nutritional stressors or disease. From a research perspective, determining the exact causes of pregnancy loss or embryonic mortality in cattle have been difficult, due to limitations of accurately determining early gestation pregnancy status. Until methods that precisely determine embryo success early in gestation are available, our understanding of in vivo pregnancy loss will lack clarity necessary to develop management strategies to decrease such loss. In this review, we will briefly discuss the pivotal periods of pregnancy loss affecting beef and dairy cattle, methods and technologies to determine pregnancy status and embryo viability and potential opportunities to decrease reproductive failure.

Forty-five non-lactating, pregnant Holstein animals (18 heifers and 27 multiparous cows; BW = 561±114 kg; BCS = 2.9±0.3; days pregnant = 110±56 d) were stratified by initial BW and BCS, and randomly assigned to receive daily (as-fed basis) 0.50 kg of ground corn plus 0.22 kg of kaolin (CON), calcium salts of saturated fatty acids (SFA) or polyunsaturated fatty acids (PF) for 14 d. Blood samples were collected on days 0, 7 and 14, immediately prior to (0 h) and 3, 6, 9 and 12 h after feeding, to determine the serum concentrations of P4 and insulin. No treatment effects were detected for serum concentrations of P4 (5.52, 6.13 and 5.63±0.41 ng/mL for CON, SFA and PF, respectively). No treatment effects were detected for serum concentrations of insulin (11.5, 10.5 and 10.1±1.43 µIU/mL for CON, SFA and PF, respectively). Heifers had greater serum concentrations of P4 than multiparous cows (6.35 vs. 5.16±0.42 ng/mL), but lower serum concentrations of insulin (7.0 vs. 14.4±1.49 µIU/mL). Feeding 0.22 kg of calcium salts of polyunsaturated fatty acids is not sufficient to increase the serum concentrations of P4 and insulin of non-lactating, pregnant dairy cows.

Esta pesquisa avaliou o efeito da separação mãe-ninhada sobre o desempenho reprodutivo de coelhas lactantes e ponderal das ninhadas até aos 70 dias de idade. Examinaram-se 415 exposições ao macho de 157 fêmeas lactantes distribuídas em dois grupos: controle, com livre acesso ao ninho, e tratado, cujo acesso bloqueou-se entre o sétimo e o nono dias pós-parto, durante as 39 horas que precederam a cobrição. Das 415 exposições ao macho, 387 resultaram em cobrições e 264 em partos. As fêmeas tratadas, de quinta lactação em diante, apresentaram receptividade e taxa de parição, respectivamente, 6,7% e 10,8% maiores em comparação às fêmeas do grupo controle. Não se constatou efeito da interação tratamento x ordem de lactação, ou do tratamento, com respeito ao número de láparos/ninhada à desmama e nos 70 dias de idade. Em ninhadas de primíparas, a taxa de mortalidade da separação até 70 dias de idade foi maior no grupo tratado, em relação ao controle (0,248±0,047 vs. 0,120±0,047). O peso total da ninhada à desmama foi inferior no grupo tratado, do que no controle (5.753±93 g vs. 6.222±89 g) em todas as ordens. Todavia, não se observou diferença no peso total ou médio da ninhada nos 70 dias de idade. O tratamento também reduziu o peso individual à desmama (912,4±4,9 g vs. 962,7±4,5 g) em todas as ordens de lactação, entretanto, elevou o ganho de peso médio diário pós-desmama (32,25±0,19 g/d vs. 31,44±0,17 g/d), proporcionando a ocorrência de ganho compensatório neste período. Pode-se recomendar a separação temporária mãe-ninhada para melhorar o desempenho reprodutivo de coelhas lactantes multíparas; mas deve ser evitada para as primíparas, devido à elevação da taxa de mortalidade das ninhadas.

The objective was to evaluate the effect of temporary mother-litter separation on the reproductive performance of lactating does and growth performance of their litters up to 70 days of age. A total of 415 presentations of 157 lactating does assigned to two groups: control, with free nest access, and treated, whose nest access was closed during the 39 hours that preceded mating, were analyzed. From the 415 presentations, 387 resulted in matings and 264 in parturitions. Does of the treated group, from fifth and further lactations, had sexual receptivity and parturition rate, respectively, 6.7% and 10.8% higher than those females of the control group. No treatment by lactation order interaction, or treatment effects, were detected on number weaned and number of young per litter at 70 days. In litters of primiparous does, mortality rate from separation up to 70 days of age was higher in the treated group (0.248±0.047 vs. 0.120±0.047). Litter weaning weight was lower in the treated group compared to the control group (5,753±93 g vs. 6,222±89 g), for all lactation orders, but no differences were detected in total and average 70-d weights between groups. Treatment also reduced individual weaning weight (912.4±4.9 g vs. 962.7±4.5 g) for all lactation orders, but increased postweaning average daily gain (32.25±0.19 g/d vs. 31.44±0.17 g/d), favoring the occurrence of a compensatory weight gain in this period. Temporary mother-litter separation may be recommended to improve reproductive performance of lactating multiparous does, but should be avoided for primiparous due to the increased mortality rate of their litters.