Diagnoses of pregnancy were made on 110 Hereford cross Friesian and 69 blue grey (white shorthorn cross Galloway) cows between 92 and 202 days after last service using a real-time ultrasonic scanning instrument with a 3.5 MHz rectal transducer. Of the 174 cows which subsequently calved, one was wrongly diagnosed as non-pregnant. Of the five cows which did not subsequently calve two were diagnosed as pregnant and may in fact have been pregnant at the time of scanning. The overall level of accuracy of pregnancy diagnosis was 98.3 per cent. In further trials with 16 Hereford cross Friesian and 16 blue grey cows scanned at regular intervals between 20 and 140 days of gestation, pregnancy was diagnosed with confidence from 30 days, and relationships were established whereby gestational age could be estimated from measurements of certain uterine and fetal dimensions. Crown-rump length provided the most precise estimate of gestational age (residual sd +/- 4.5 days) and uterine diameter the least (+/- 12.6 days) with head length and the diameters of trunk, head and nose being intermediate (+/- 6.9 to 8.7 days).

An experiment was conducted to examine factors affecting the length of the post-partum anoestrous period and associated effects on LH, FSH and prolactin. Forty-six cows (24 Hereford × Friesian and 22 Blue-Grey) ranging in body condition score at calving from 1·50 to 2·75 were used. They were individually fed chopped barley straw and concentrate at either 50 (low) or 91 (high) MJ metabolizable energy per day from calving. At 34 days post partum half the cows were separated from their calves for 48 h. The duration of the post-partum anoestrous period was estimated from progesterone concentrations in thrice weekly blood samples. Blood samples were collected every 20 min for 10 h periods immediately prior to calf separation, during the last 10 h of calf separation and 1 week later. All samples were analysed for LH, and every third sample was analysed for FSH and prolactin.There were no significant effects of genotype, feeding level or calf separation on the length of the post-partum anoestrous period. There was a negative association between body condition score at calving and the length of the anoestrous period, with each unit increase in body condition score reducing the anoestrous period by 43 (s.e. 20) days. There was some evidence that feeding level affected the number of thin cows (body condition score ≤2·25 at calving) which were still acyclic at the end of the experiment, but not the number of fat cows (body condition score ≥2·5 at calving).FSH levels were not affected by any of the factors examined. Prolactin concentrations were higher in fatter cows, in cows on the higher level of feeding and in Blue-Grey cows. Prolactin concentrations decreased during the period of calf separation. Genotype and feeding level had no effect on LH concentration or LH pulse frequency. LH pulse frequency was increased (P < 0·05) during the period of calf separation, but there was no effect 1 week later. There was a significant positive relationship between LH puise frequency and body condition score at calving in two of the three sampling periods.It is suggested that the effect of body condition on the duration of the post-partum anoestrous period i s mediated through effects on LH pulse frequency.

An experiment was conducted to examine the effects of body condition at calving and feeding level post partum on the duration of the post-partum anoestrous period in beef cows. Forty-seven cows were used in each of 2 years. Cows were fed differentially before calving to achieve two levels of body condition at calving in November and December and were then fed at one of two levels of feeding post partum in a 2 X 2 factorial experiment. At calving, mean body condition scores were 2-85 (F) and 2-23 (T) (P < 0-001) while live weights were 521 kg and 457 kg (P < 0-001) for F and T cows respectively. After calving metabolizable energy intakes were 111 and 118 M]/ day (H) or 56 and 64 M]/day (L) in years 1 and 2 respectively. The H cows maintained live weight during the first 61 days of lactation while the L cows lost live weight (0-0 v. -1-1 kg/day, P < 0-001). The number of cows still acyclic on 1 May each year was higher (P < 0-01) on the TL treatment (10/24) compared with the other treatment combinations (FH: 2/22; FL: 5/22; TH: 2/24). The effect of level of feeding on the duration of the anoestrous period was significant in the T cows (89 v. 116 days for TH and TL cows respectively; P < 0-01) but not in the F cows (80 v. 89 days for the FH and FL cows respectively; P > 0-05). At 3 weeks post partum LH pulse frequency was higher in F than in T cows and tended to be higher in H than in L cows. At 6 and 9 weeks post partum LH pulse frequency was higher in H than L cows. LH pulse amplitude was higher in F than T cows at 3 weeks post partum and tended to be higher at 6 weeks post partum. It is concluded that both body condition at calving and feeding level after calving influence the duration of the post-partum anoestrous period with the effect of feeding level being particularly pronounced in thin cows.

The response of continuously stocked sptingcalving beef cows and calves to a range of sward surface heights was determined. Mean sward heights of 4-5, 60, 70, 9 1 and II 0 cm (treatments A to E respeclively) were maintained from mid-May to mid-August (Period I) and treatments C, D and E continued until the end of September (Period 2), during which time mean sward heights were 5-4, 7-8 and 92 cm respectively. Hereford x Friesian or White Shorthorn-X Galloway cows with their Charolais-cross calves were used, with 9, 6, 6, 5 and 9 cows on treatments A to E respectively. During Period 1 the mean liveweight gains of cows were -0-52, -0 05,0-32,0 75 and0 40 (s.e.d. 0167) kgd"' on treatments A to E respectively and during Period 2. -0-31, 057 and 0 59 (s.e.d. 0153) kgd-' for treatments C, D and E respectively with maximum cow liveweight gain at sward heights of 8 to 10 cm. Calf liveweight gains were 0 88,0 91,0 98, 1 04 and 1 06 (s.e.d. 0 068) kg d -' in Period 1 for treatments A to E respectively and 0 98, I -22 and 1 35 (s.e.d. 0067) kg d"' in Period 2 for treatments C, D and E. The percentage of area infrequently grazed was generally less than 20% on treatments A to D, but on treatment E it was more than 40% for 6 weeks after turnout and thereafter remained between 20 and 40%. Maximum calf liveweight gain per hectare was achieved on the shorter swards, but maximum Correspondence: Dr I. A. Wright, Macaulay Land Use Research Institute, Penlliind field, RosUn, Midlothian, EH26 OPY.total liveweight gain of cows and calves per hectare occurred on treatment D. It is concluded that for maximum cow and calf performance on continuously stocked pastures, sward height should be maintained at no more than 8 cm in spring and early summer and then increased to 9 to 10 cm later in the grazing season.

Three hundred pregnant beef cows between 35 and 125 days of gestation were scanned ultrasonically and their calving dates were predicted from measurements of fetal parts. The mean difference between the actual and predicted calving dates was 0.9 day with a standard deviation of 9.0 days. The accuracy and precision of the prediction of calving date were sufficient to be of benefit in the management of cows in late pregnancy and at calving.

Thirty-nine Hereford × Friesian autumn-calving cows (mean calving date 17 September) and their Charolais-cross calves were used in a 2 × 2 × 2 factorial experiment to assess the effects of feeding level in winter and sward height in summer on intake and performance. Mean estimated metabolizable energy intakes during winter (30 October to 6 May) were 63 (L) or 92 (H) MJ/day. Two sward heights, 4·8 (SI) or 7·6 (Tl) cm, were imposed from turn-out to weaning on 3 July, and a further two sward heights, 4·7 (S2) or 8·0 (T2) cm, from weaning to housing on 1 October. At turn-out the H cows were 17 kg heavier (P > 0·05) than the L cows and their calves were 30 kg heavier (P < 0·01). Cow herbage intakes were significantly higher on the Tl and T2 treatments compared with the SI and S2 treatments as were live-weight changes: 0·94 v. –0·01 kg/day (P < 0·001) for Tl and SI treatments and 0·96 v. –0·18 kg/day (P < 0·001) for T2 and S2 treatments respectively. Calves on the Tl treatment had higher live-weight gains than those on the SI treatment (1·40 v. 0·63 kg/day; P < 0·001). After weaning the SI cows had significantly higher herbage organic matter intakes than the Tl cows (P < 0·05) and had significantly higher live-weight gains (0·51 v. 0·28 kg/day; P < 0·05). Calving difficulty and calf birth weight were not affected by any of the treatments. The results demonstrate that both previous and current level of nutrition have an effect on cow performance. When cows are turned out to pasture at body condition scores of 2·25 to 2·5, the sward heights recommended for spring-calving cows are equally appropriate for autumn-calving cows.

The effect of body condition on hypothalamic and pituitary function in post-partum suckled beef cows was studied. Thirty-eight Blue-Grey cows were calved at a body condition score of either 2·35 (L) or 2·80 (H), fed to maintain live weight and body condition thereafter and ovariectomized at either 5 or 9 weeks post partum. The H cows had higher LH pulse frequencies before ovariectomy (0·36 v. 0·28 pulses per h; P < 0·05) and 15 days after ovariectomy (0·86 v. 0·72 pulses per h; P < 0·01), indicating a direct effect of body condition on GnRH release from the hypothalamus. Body condition had no effect on the ability of the pituitary to release LH in response to a physiological dose (2·5 u.g) of GnRH in entire or ovariectomized cows at 5 or 9 weeks post partum. The magnitude of the increase in circulating levels of LH following GnRH injection was greater at 9 weeks compared with 5 weeks post partum (2·23 v. 1·73 u.g/1; P < 0·001) in entire cows, but there was no difference between 5 and 9 weeks in ovariectomized cows. Following ovariectomy there was a 2·5-fold increase in LH pulse frequency within 15 days and LH pulse frequency approached 1 pulse per h in all treatments groups. It is concluded that both the hypothalamus and the pituitary are capable of functioning normally by 5 weeks post partum in suckled beef cows, that the pulsatile release of GnRH from the hypothalamus is inhibited, possibly due to a very high sensitivity to oestradiol, and that the sensitivity of the pituitary to the negative feedback effect of oestradiol may decrease with time post partum.

Two experiments were conducted to determine whether female to female influences could reduce the duration of the post-partum anoestrous period in beef cows. In experiment 1, cows were housed from calving, either in individual stalls, which precluded physical contact with other cows (treatment I; no. = 19) or as a group, with a cow in oestrus introduced to the group twice per week (treatment G; no. = 18). The percentage of cows cycling by day 50 post partum was similar for both treatments, but at 91 days post partum was significantly higher (P < 0-05) in the G than in the I cows (89% v. 58%). In experiment 2, cows were housed in individual stalls from calving and exposed twice per week to either cervical mucus collected from cows in oestrus (treatment M; no. = 21) or distilled water (treatment W; no. = 24). The percentage of cows cycling by 70 days post partum was similar in both treatments but by 130 days there were significantly more (P < 0-05) M cows cycling (86% v. 58%). In neither experiment were LH profiles at 22,43 or 64 days influenced by treatment.The results indicate that cervical mucus of cows in oestrus contains pheromone(s) which can reduce the postpartum anoestrous period in beef cows with extended anoestrous periods.