Evaluation of beef cow and calf separation systems to improve reproductive performance of first-calf cows

Abstract

A two-year study was conducted with the objective to compare the effects of a traditional 48-h calf withdrawal to early-weaning and repeated 48-h calf withdrawals on postpartum interval and measures of performance of first-calf cows. A total of 112 primiparous, Brahman×British cow–calf pairs were randomly allotted to three treatments over two consecutive years: early weaning (EW; permanent cow and calf separation); interval weaning (IW—48-h calf withdrawal; five times, 20 days apart); and control (CON; single 48-h calf withdrawal). Early-weaned calves were kept in an annual ryegrass (Lolium multiflorum) pasture and were fed supplemental concentrate (16% crude protein) daily at 1% of body weight. During the 48-h calf withdraw IW- and CON-calves were provided hay, water and free-choice access to the same concentrate supplement. Treatments were initiated at the start of a 90-day breeding season (average days postpartum=97±19). Blood samples were collected over 90 days on 10-day intervals for determination of progesterone concentrations. Resumption of cyclicity was defined as two consecutive samples with concentrations of progesterone ≥1.5ng/mL. Cow body weight was determined at the start (day 0), middle (day 41), and end (day 90) of the study, and cow body condition score was estimated using a nine-point scale where 1=emaciated and 9=obese on same days, only on year 2. Calf body weight was determined at the start and end of the study. Pregnancy was diagnosed by transrectal ultrasonography at approximately 45 days after the end of the breeding season. Cow body weight and body condition score at the beginning of the breeding season did not differ (369±38.2kg and 4.5±0.59, respectively); however, by day 90 body weight was greater (P<0.01) and body condition score tended to be greater (P=0.08) for EW versus IW and CON (385, 356, and 359kg; SEM=2.6; and 4.6, 4.1, and 3.9; SEM=0.20 for EW, IW, and CON cows, respectively). Calf BW was also greater (P<0.01) for EW calves versus IW and CON calves at the end of the study (170, 127, and 132kg for EW, IW, and CON calves, respectively; SEM=3.1). Cows in the EW and IW treatments had resumption of cyclicity earlier than CON cows (average days to resume cyclicity=65, 67, and 75 for EW, IW, and CON cows, respectively; SEM=0.2). By day 20 of the breeding season (corresponding to an average of 117 days postpartum), more (P=0.06) EW cows were cycling than CON-cows with IW cows intermediate. Cows exposed to IW had a greater (P=0.05) pregnancy rate than CON cows. Compared to a traditional, single-time, 48-h calf withdrawal, repeated 48-h calf withdrawal resulted in greater cow pregnancy rate with a reduced period of postpartum anestrus.