Calving probability in the first and second reproductive years of beef heifers that reached the recommended body weight at first breeding season

Abstract

The objective was to evaluate factors that influence calving probability in the first and second reproductive years of beef heifers that reached the minimum recommended body weight (BW) in the first breeding season. Two hundred twentyseven 24-month-old Charolais × Nellore heifers that mated between 2003 and 2012 were analyzed. The parameters evaluated were: year effect; individual and maternal heterozygosis; percentage of Charolais genotype; average daily gain (ADG) from weaning to the end of the first breeding season; BW at 18 and 24 months of age, end of breeding season, parturition, and weaning; Julian date of calving; and adjusted calf weight at weaning. These variables were subjected to logistic regression. Calving rates in the first and second reproductive years were 58.1 and 49.5%, respectively. Performance until the end of the first breeding season, BW before the first breeding season, and individual heterozygosis affected the calving probability in the first breeding season. In the second breeding season, BW variation from the first breeding season and calving, Julian date of calving, and BW at the end of the second breeding season influenced calving probability. Until the end of the first breeding season, ADG of beef heifers responded positively to the calving probability, even after reaching the usually recommended BW for the first breeding season. Primiparous cows calving at the beginning of the breeding season and gaining more BW between the first and second breeding season are more likely to give birth in the second breeding season.

Body mass index at calving on performance and efficiency of Zebu cow herds

“…On the contrary, with the use of postpartum supplementation (Farias et al, 2018a,b) or calcium salt supplementation in the pre-and postpartum periods in adult cows (Vara et al, 2020), pregnancy rates are influenced by cow body size. The probability of pregnancy is directly related to the nutritional status of the cow as well as to its current energy balance, and its prolongation is harmful to the subsequent reproductive performance (Pacheco et al, 2020a;Torres, Tineo, & Raidan, 2015). In the present study, the supplementation provided in the postpartum period may have influenced the results, as the cows were not subjected to a drastic negative energy balance, which led to satisfactory reproductive performances regardless of BMI class.…”

“…Cows that gain weight between mating and calving are more likely to repeat pregnancy, especially during the growing phase (Pacheco et al, 2020a). However, in pasture-based production systems, fluctuations in the quantity and quality of forage can compromise the nutritional status of dams at some times of the year (Gutiérrez et al, 2014).…”

“…Pregnancy in beef cows is influenced by several factors (Pacheco et al, 2020a). A larger body size can have negative effects on reproductive performance, as compared with smaller sizes, when the postpartum feeding system is not ideal (R. M. Silva et al, 2015) or when the cows are primiparous and have their first lactation while still growing (Pacheco et al, 2019b;Vaz et al, 2020a).…”

“…Nutritional restrictions during pregnancy and lactation can affect the growth and development of muscle fibers and marbling cells, which are formed in the prenatal period, compromising animal development and meat quality (Du et al, 2010;Gutiérrez et al, 2014). In addition, the likelihood of pregnancy recurrence may be reduced (Pacheco et al, 2020a).…”

Effect of the performance, calving date and lactation period on the probability of pregnancy in beef cows

“…The pregnancy rate in cattle is a variable that strongly impacts the productive efficiency of breeding herds (Burns et al, 2010;Pacheco et al, 2020). The intensification of production systems passes through stages requiring an increase in the pregnancy rate (Mulliniks et al, 2020) and reproductive physiology related to herd management and nutrition (Klein et al, 2021).…”