No abstract

Nutrition and suckling are largely recognised as the most important factors affecting the postpartum period and consequently the reproductive efficiency of beef cattle. The aim of this study was to evaluate the effects of body condition score (BCS) and suckling restriction with and without the presence of the calf on milk production, reproductive efficiency and calf performance. Sixty-three crossbred (Angus · Hereford) multiparous cows were managed to maintain different BCS at calving and thereafter (low vs moderate; L, n = 31 and M, n = 32). Within each group of BCS (L and M) at week 9 postpartum (66 AE 0.88 days postpartum) cows were assigned to three suckling treatments (ST): (i) suckling ad libitum (S, n = 20); (ii) calves fitted with nose plates during 14 days remaining with their dams (NP, n = 22); and (iii) calves were completely removed from their dams for 14 days, and thereafter returned (CR, n = 21). Milk production was assessed by milking procedure at Day 65 (the day before onset of ST) and every 20-22 days until the end of the experiment. Cows were bled via jugular venipuncture every 28 days from Day -98 (Day 0 = calving) until Day 66. From Day 66 cows were bled every 7 days until the end of the mating period (Day 128). Concentrations of progesterone, non-esterified fatty acids and b-hydroxybutyrate acid and insulin were measured. Presence of corpus luteum (CL) was recorded and maximum follicle diameter was measured in all cows from the onset of the ST (Day 66) and during the following 4 weeks (until Day 94) in a weekly frequency. At Day 94, more cows (P < 0.001) in NP and in CR had CL compared with S cows (68, 57 and 21% for NP, CR and S, respectively). At that time, more cows in M-BCS presented CL than cows in L-BCS (77 vs 25; P < 0.0001). Within M-BCS, there were no differences in milk production between ST groups, while L-BCS cows with NP or CR produced less milk than S cows. Calf liveweight at weaning was 159.3 AE 3.1, 150.1 AE 2.9 and 147.0 AE 3.1 kg for S, NP and CR, respectively (P < 0.001). Suckling restriction with and without the presence of the calf had similar effects on reproductive performance, milk production and calf growth, while BCS interacted with ST to influence milk production. These results indicate that temporary suckling restriction could be an excellent management tool to increase reproductive performance of cows in moderate condition.

Early weaning is used to advance postpartum ovulation in beef cows, but triggers a stress response, affecting cows' and calves' welfare. Our aim was to compare the response to early weaning in multiparous and primiparous cows. Seventy-one days after birth, calves from 14 primiparous and 11 multiparous cows were weaned. Since birth, cow's body weight (BW), body condition (BC), milk yield and calves' BW were recorded. Basophil/neutrophil relationship, total protein and albumin concentrations were measured before and after weaning. The distance between each cow and its calf before weaning, as well as main behaviors of the cows before and after weaning were recorded using 10 min scan sampling. BW and BC were greater in multiparous than in primiparous cows ( P , 0.0001 for both). There was an interaction between parity ( P 5 0.004) and gender of the calf ( P 5 0.007): both BW and BC were greater in multiparous than primiparous cows, but multiparous cows with male calves had lower BW and BC than those with females ( P , 0.001 for both variables). Milk yield was greater in multiparous than in primiparous cows ( P 5 0.02), and there was an interaction, with greatest milk yield in multiparous cows that calved males ( P 5 0.02). Total protein blood concentration increased with time ( P , 0.0001), similarly in both groups. Albumin concentration profiles were similar despite parity, and decreased since 10 days after weaning ( P , 0.0001). Basophil/neutrophil ratio was not affected by parity, and increased the day of weaning, remaining high until day 10 ( P , 0.05). Frequency of standing decreased during the 2 days after weaning, with a greater decrease in multiparous than in primiparous cows ( P , 0.0001). Pacing increased after weaning ( P 5 0.001), but increased significantly more in multiparous cows ( P 5 0.006), with a significant time after weaning by parity interaction ( P 5 0.01) reflected in greater frequencies in multiparous cows in the 2 days. Walking increased with time ( P , 0.0001), and was more frequent in primiparous cows ( P 5 0.008). Ruminating, which was less frequent in multiparous cows ( P 5 0.014), decreased and remained low during the 3 days following weaning ( P , 0.0001), but there was a significant time by parity interaction ( P , 0.0001). The frequency of vocalizations increased dramatically after weaning ( P , 0.0001), and was greater in multiparous cows ( P 5 0.006), and decreased more slowly during the 2nd and 3rd days after weaning ( P 5 0.005) in these animals. In conclusion, behavioral changes induced by weaning were greater in multiparous than primiparous cows, indicating a more intense response to cow-calf separation in the multiparous animals.

No abstract

The effects of body condition score (BCS) of 2·0 or 3·0 units at calving (low v. moderate), post-partum energy intake at 0·6 or 1·0 MJ metabolizable energy (ME) per day per kg M0·75 (low v. high) and unrestricted or restricted (once daily) suckling on the ability of cows to ovulate were studied in a 2 ✕ 2 ✕ 2 factorial design with each treatment replicated eight times. Calf isolation and restricted suckling were imposed shortly after selection of the first dominant follicle (DF) to emerge after day 21 post partum. The episodic release of LH (sampled at 15-min intervals for 10 h) was determined 48 h before and 48 h after the day calf isolation and restricted suckling commenced. Additional blood samples were collected weekly for plasma insulin determination. The mean interval from calving to first ovulation was shorter for cows in moderate than low BCS at calving (47·8 v. 57·1 days, s.e.d. = 4·50, P < 0·05), and for cows suckling once daily than for those with unrestricted suckling (42·9 v. 62·0 days, s.e.d. = 4·50, P < 0·001). Post-partum nutrition did not affect this interval. Mean LH pulse frequency prior to the start of restricted suckling was higher for cows of moderate than low BCS at calving (3·2 v. 1·6 pulses per 10 h, s.e.d. = 0·60, P < 0·05). Subsequently, LH pulse frequency was higher for cows suckling once daily than for those with unrestricted suckling (4·0 v. 2·2 pulses per 10 h, s.e.d. = 0·82, P < 0·05). More cows in moderate than low BCS ovulated the first DF to emerge after day 21 post partum (within 4 to 6 days) in response to restricted suckling (69 v. 25%, P < 0·05). LH pulse frequency prior to restricted suckling increased (P < 0·05) with plasma insulin concentration (categorized as low, < 5; moderate, 5 to 8; and high, >8 mIU per l). There were indications of interactions between suckling treatment and BCS (P < 0·08), and suckling treatment and plasma insulin concentration (P < 0·06), on LH pulse frequency, which suggested that calf restriction could alleviate the suppressive effects of under nutrition on episodic LH release. Amongst cows suckling once daily, the non-ovulating animals had fewer LH pulses prior to restricted suckling and smaller, slower growing DF, indicating an inability of the DF to respond to increased LH pulse frequency following calf restriction. Cows of moderate BCS, particularly those with moderate to high levels of plasma insulin (³ 5 mIU per l), responded favourably to restricted suckling. In contrast, excessively thin cows with low plasma insulin concentrations (<5 mIU per l), that had most to gain from restricted suckling, responded poorly.