Effects of timing of weaning on energy utilization in primiparous beef cows and post-weaning performance of their progeny1

Abstract

Early weaning is used to minimize cow nutrient requirements in situations where feed inputs are scarce or expensive. For many years, maintenance energy requirements have been assumed to be 20% greater in lactating compared with non-lactating beef cows. While not well established, maintenance energy requirements are thought to be greatest in primiparous cows and to decline with age. Consequently, early weaning primiparous cow–calf pairs should improve overall efficiency, particularly in situations where mid-to-late lactation forage or feed nutritive value is low. The objective of this study was to determine the biological efficiency of early weaning and maintenance energy requirements of lactating versus non-lactating primiparous cows. Experiments were conducted in two consecutive years using 90 primiparous cows and their calves (48 in yr 1, 42 in yr 2). Pairs were randomly assigned to one of the six pens (8 pairs/pen yr 1, 7 pairs/pen yr 2) and pens were randomly assigned to 1 of 2 treatments; (1) early weaning (130 d ± 15.4; EW, n = 6) and (2) traditional weaning (226 d ± 13.1; TW, n = 6). Late lactation cow and calf performance and feed consumption were measured for 92 d (yr 1) and 100 d (yr 2). Cows were limit-fed to meet maintenance requirements, while calves were offered ad libitum access to the same diet in a creep-feeding area. Calves were not allowed access to the cows’ feed. Cow feed intake, body condition score, body weight (BW), milk yield and composition, and calf body weight gain and creep feed intake were recorded. After accounting for lactation and retained energy, there was a trend for greater maintenance energy requirements of lactating primiparous cows (P = 0.07). From the early weaning date to traditional weaning date, calf average daily gain (ADG) was greater (P < 0.01) for TW calves. Feed and energy efficiency of the pair was improved for the TW system (P < 0.01). Greater ADG were reported for EW calves during the stocker period (P = 0.03), but there were no differences during the finishing period (P > 0.40). At harvest, BW was greater (P = 0.02) and gain to feed ratio tended (P = 0.06) to be improved for TW calves. The increased TW calf performance offset the additional maintenance costs of their lactating dams, resulting in the TW system converting total feed energy to kilograms of calf BW gain more efficiently.

Maintenance energy requirements and forage intake of purebred vs. crossbred beef cows1

“…The same study found that efficiency ratios were greater for Angus/Hereford pairs compared with other breeds of cattle that had a greater genetic propensity for growth and milk production. Similarly, Wiseman et al (2019) found for traditionally weaned and early weaned primiparous Angus and Hereford × Angus pairs, efficiencies were 40.2 and 37.0 g of calf gain to total pair energy intake, respectively. It is important to note that both Jenkins et al (1991) and Wiseman et al (2019) offered ration ad libitum to calves while calf feed intake was restricted in the current experiment.…”

“…It is possible that potential differences in maintenance requirements due to age are diluted in the current experiment because 2- and 3-yr-old cows were comingled. For example, in a previous study using similar techniques and a similar diet, Wiseman et al (2019) reported maintenance requirements of 107 kcal ME/kg BW 0.75 in primiparous cows from the same herd.…”

“…During the trial, milk yield was measured on day 26 and at 28-d intervals thereafter. The procedure described by Wiseman et al (2019) was used. Cows were milked with a portable milking machine (Portable Vacuum Systems, Springville, UT) and a double separation protocol was employed to allow for the standardization of milk production across all dams.…”

“…Maintenance energy requirements were defined as the amount of feed energy that resulted in no net gain or loss of body tissue energy ( NASEM, 2016 ). Maintenance requirements were determined using calculations described by Wiseman et al (2019) with the following modifications. Efficiency of the mobilization of retained energy (weight loss) was assumed to be 80% of NE m ( NASEM, 2016 ) and the retention of energy (weight gain) was assumed to be 68% of NE m ( Freetly, 2019 ).…”

“…Directly after the conclusion of the dry-lot maintenance study the 8 cow–calf pairs were moved to experimental pens. The feeding and sample collection protocol are described in detail by Wiseman et al (2019) . Daily diet samples were collected at 0700 each day.…”