by Caleb Weiss, Ph.D. Cow/Calf Product Manager
Calving difficulty increases the risk for neonatal death, cow mortality, labor, and veterinary costs and can represent a large loss for beef cattle producers. Because birth weight is positively associated with dystocia, it can be a major cause of these losses. Many factors can influence calf birth weight and calving difficulty; including cow size, body condition, age, genetic heritability, breed of dam and sire, gestation length, calf sex, number of fetuses, environmental temperature, and nutrition. Of these, meeting the nutritional needs for pregnancy can be proportional to calf birth weight as production-oriented tissues such as fetal muscle and adipose tissue that form in utero rely on this nutrient supply.
Calf birth weight is not substantially influenced if cows are maintained in an adequate plane of nutrition. According to the NRC (1996, 2000), calf birth weights are relatively unchanged when cows remain between a body condition score (BCS) of 3.5 to 7 and can be positively related below a BCS of 3.5 and inversely related to BCS when above a 7. This would suggest that feeding cows a restricted diet during late pregnancy would result in lighter calves at birth compared to cows with adequate nutrition. Researchers have investigated the effects of underfeeding during late pregnancy in an attempt to reduce birth weights and calving difficulty. These results suggest that the nutritional restrictions would need to be extremely severe to reduce birth weights and may actually increase the incidences of dystocia. This would not be recommended due to the negative effects that underfeeding can have on placental and fetal development. Poor cow nutrition during the latter stages of pregnancy can result in decreased fetal muscle fiber size and number, reduced adipocyte deposition, and decreased immunoglobulin absorption. These factors can have a lifelong effect on the performance of the calf. Additionally, maternal undernutrition can also lead to other issues including increased calving difficulty due to the dam being too weak and undernourished to deliver a calf as well as decreased calf survival, longer postpartum interval, and reduced milk supply and quality which can negatively impact calf health and weaning weights. Inversely, overfeeding cows to the point of obesity may increase the incidence of dystocia.
Reducing the nutrient intake of cows prior to calving will not substantially reduce birth weights of calves and may increase calving difficulty, reduce postpartum reproductive performance, and decrease calf productivity. Producers should understand their cows’ nutrient requirements to prevent under or over feeding and should focus on other factors such as genetic selection to influence birth weights. For more information, please contact your local QLF representative.