Weaning and post-weaning performance by fall-born beef calves weaned on different dates in the spring from Neotyphodium coenophialum-infected tall fescue pastures

Effects of early weaning on the reproductive performance of suckled Nelore cows in the subsequent breeding season

This study aimed to evaluate the effects of early weaning (EW) on body composition, hormone concentrations and metabolites, and reproductive performance of Nelore cows in the subsequent breeding season (BS). Suckled cows that became pregnant by timed-AI (TAI) in the 2020-BS were exposed in 2021 to early weaning at 150 d (27 primiparous [PRI] and 74 multiparous [MUL]) or conventional weaning (CW) at 240 d postpartum (30 PRI and 77 MUL). Body weight (BW) and body condition score (BCS) were determined at 2020-BS, EW, CW, prepartum, and 2021-BS. Blood samples were collected at EW, CW, prepartum (54.75 ± 0.56 d prepartum), and 2021-TAI and assayed for insulin-like growth factor-1 (IGF-I), non-esterified fatty acid (NEFA), and β-hydroxybutyrate (BHB) concentrations. In 2021-BS, cows were exposed to a P4/E2-based protocol for TAI at day 0 (D0), and a second TAI was performed at D22 in females detected with luteolysis (D20) by Doppler ultrasound. The presence of corpus luteum (CL) on D10, estrous expression, and dominant follicle (DF) diameter, and blood perfusion (BP) on D2 and D0 were determined. Data were analyzed by ANOVA or logistic regression of SAS as a 2 × 2 factorial with main factors of parity (PRI or MUL) and weaning strategy (EW or CW). An interaction of parity and weaning strategy was not observed (P > 0.1), but the weight (kg) and BCS were greater (P < 0.05) in MUL cows at the five timepoints, and EW cows were heavier than CW at the moment of CW (541 vs. 493 kg; and 5.3 vs. 4.3), prepartum (551 vs. 506 kg; and 5.2 vs. 4.4) and 2021-BS (475 vs. 450 kg; and 4.5 vs. 3.7). Plasma urea concentration at 2021-BS was greater (P = 0.01) for PRI than for MUL. A parity-by-time interaction was observed (P ≤ 0.05) for concentrations of IGF-I, NEFA, and BHB. PRI cows had greater (P ≤ 0.05) concentrations of IGF-I at EW and greater (P ≤ 0.05) prepartum concentrations of NEFA and BHB than MUL cows. The proportion of cows with CL at D10 was not affected (P > 0.1) by weaning but was greater (P < 0.05) in MUL than in PRI cows (40.4 vs. 15.7%). The diameter of DF and proportion of BP on D0 were greater (P < 0.05) in EW cows than in CW cows. The pregnancy rate (P/AI, %) at the first TAI was greater (P < 0.05) in EW cows (60% vs. 45%), whereas no difference (P > 0.1) was observed at the second TAI. Cumulative P/AI (first and second TAIs) was greater (P < 0.05) in EW cows (81% vs. 63%). In conclusion, weaning at 150 d in Nelore cattle is a strategy to successfully recover the parous cow's body condition and to improve pregnancy success in the next BS, regardless of the cow's parity order.

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

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.

Performance by spring and fall-calving cows grazing with full, limited, or no access to toxic Neotyphodium coenophialum-infected tall fescue

Replacing toxic, wild-type Neotyphodium coenophialum-infected tall fescue (E+) with nontoxic, N. coenophialum-infected tall fescue (NE+) has improved cow performance, but producer acceptance of NE+ has been slow. The objective was to compare performance by spring- and fall-calving cows grazing either E+ or NE+ at different percentages of the total pasture area. Gelbvieh×Angus crossbred cows (n=178) were stratified by BW and age within calving season and allocated randomly to 1 of 14 groups representing 5 treatments for a 3-yr study: i) Fall-calving on 100% E+ (F100); ii) Spring-calving on 100% E+ (S100); iii) Fall-calving on 75% E+ and 25% NE+ (F75); iv) Spring-calving on 75% E+ and 25% NE+ (S75); and v) Spring-calving on 100% NE+ (SNE100). Groups allocated to F75 and S75 grazed E+ until approximately 28 d before breeding and weaning, then were then moved to their respective NE+ pasture area for 4 to 6 wk; those allocated to F100, S100, and SNE100 grazed their pastures throughout the entire year. Samples of tall fescue were gathered from specific cells within each pasture at the time cows were moved into that particular cell (∼1 sample/mo). Blood samples were collected from the cows at the start and end of the breeding season. Stocking rate for each treatment was 1 cow/ha. Forage IVDMD, CP, and total ergot alkaloid concentrations were affected (P<0.05) by the treatment×sampling date interaction. Hay offered, cow BW, and BCS at breeding, end of breeding, and at weaning were greater (P<0.05) from fall-calving vs. spring-calving. Cow BW at weaning was greater (P<0.05) from F75 and S75 vs. F100 and S100. The calving season×NE+ % interaction affected (P<0.05) calving rates. Preweaning calf BW gain, actual and adjusted weaning BW, ADG, sale price, and calf value at weaning were greater (P<0.05) from fall-calving vs. spring-calving and from SNE100 vs. S75 except for sale price which was greater (P<0.05) from S75 vs. SNE100. Cow concentrations of serum prolactin at breeding and serum NEFA at the end of breeding were affected (P<0.05) by the calving season×NE+ % interaction. Serum Zn and Cu concentrations from cows were affected (P<0.05) by calving season. A fall-calving season may be more desirable for cows grazing E+, resulting in greater calving rates, cow performance, and calf BW at weaning, whereas limited access to NE+ may increase calving rates, serum prolactin, and NEFA concentrations during certain times in the production cycle, particularly in spring-calving cows.