Ovulation of the first dominant follicle arising after day 21post partumin suckling beef cows

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.

Optimising reproductive performance of beef cows and replacement heifers

“…In the study of Stagg et al, (1998) a total of 43%, 65% and 90% of cows had ovulated by 80 days postpartum for cows with ad libitum calf access, suckled once daily suckling with calves Diskin and Kenny penned adjacent to their dams and suckled once daily suckling with calves isolated from their dams, respectively. Interestingly, in both of the studies of Stagg et al (1998) and Sinclair et al (2002) a small proportion (circa 15%) of cows failed to respond to the removal of the suckling/maternal calf bond and showed no increase in LH pulse frequency and no evidence of an increase in the circulating concentrations of oestradiol. These 'non-responders' typically had prolonged postpartum anoestrous intervals and could be described as being in 'deep anovulatory anoestrus' (Sinclair et al, 2002).…”

“…Interestingly, in both of the studies of Stagg et al (1998) and Sinclair et al (2002) a small proportion (circa 15%) of cows failed to respond to the removal of the suckling/maternal calf bond and showed no increase in LH pulse frequency and no evidence of an increase in the circulating concentrations of oestradiol. These 'non-responders' typically had prolonged postpartum anoestrous intervals and could be described as being in 'deep anovulatory anoestrus' (Sinclair et al, 2002). In the latter study there was evidence of an association between low circulating concentrations of insulin, during the early postpartum period, and the failure to record an ovulatory response to calf separation/isolation thus emphasising the importance of nutrition as a regulator of PPI.…”

“…Use of calf separation/isolation to stimulate recommencement of oestrous cycles The studies of Stagg et al (1998) and Sinclair et al (2002) clearly show that the use of calf separation/isolation, commencing at around day 30 postpartum, results in an immediate (within 2 to 5 days) increase in LH pulse frequency with about 85% of cows responding by ovulating the first dominant follicle that develops and is exposed to this increased LH pulse frequency. For optimal effect, the data of Stagg et al (1998) would clearly imply that calves must be isolated from their dams with no tactile contact permitted between them.…”

Parturition to resumption of ovarian cyclicity: comparative aspects of beef and dairy cows

“…Interestingly, in the small proportion of cows that fail to respond to the removal of the suckling/maternal calf bond show no increase in LH pulse frequency, and no evidence of an increase in the circulating concentrations of oestradiol. These non-responders typically had prolonged postpartum anoestrous intervals and could be described as being in "deep anovulatory anoestrus" (Sinclair et al, 2002).…”

“…Plasma insulin concentrations are influenced by both BCS and level of nutrition (Vizcarra et al, 1998), and may serve as a more sensitive indicator of nutritional status than BCS. In a transnational study, Sinclair et al (2002) showed that postpartum anoestrous beef cows with low (<5 mIU/l) plasma concentrations of insulin were unable to ovulate a dominant follicle in response to restricted suckling, unlike cows with higher (>5 mIU/l) plasma concentrations of insulin, notwithstanding an increase in LH pulse frequency. The results of that study are consistent with those of Gong et al (2001Gong et al ( , 2002 who showed that dairy cows fed a diet, which increased circulating concentrations of insulin during the first 50 days postpartum had shorter postpartum anoestrous intervals, independent of any effects on LH or FSH and without affecting milk yield or energy balance.…”