Four experiments were carried out to examine the effects of administration of pFSH (Vetrepharm) from Day 3 of the estrous cycle in conjunction with PG on Day 5 on follicular populations and ovulation rate in heifers. In Experiment 1, 47 heifers were allocated to 1 of 4 treatment groups (n = 11 to 12 per group): a) control, b) 1.5 mg pFSH, c) 2.0 mg pFSH or d) 2.5 mg pFSH until estrus. Heifers assigned to the 3 treatments had a higher ovulation rate than the controls (P < 0.05). In Experiment 2, 45 heifers were allocated to 1 of 5 treatment groups (n = 8 to 10 per group): a) control, b) 1.0 mg pFSH until PG, c) 1.0 mg pFSH until estrus, d) 1.5 mg pFSH until PG or e) 1.5 mg pFSH until estrus. From Day 5, heifers assigned to pFSH treatments had more large follicles than the controls (P < 0.05). There was no effect of treatment on the incidence of twin ovulations. In Experiment 3, 43 heifers were assigned to 1 of 3 groups (n = 11 to 16 per group): a) control, b) 1.0 mg pFSH until estrus or c) 1.5 mg pFSH until estrus. At slaughter, 14 d after administration of PG, the incidence of twin ovulations was 0/11, 7/16 and 8/16 for Groups a, b and c, respectively (P = 0.011). In Experiment 4, pFSH (1.5 mg) was administered to 3 groups during the development of the first dominant follicle: a) growth phase (n = 19); b) static phase (n = 17); and c) decline phase (n = 17). All pFSH-treated heifers had a higher ovulation rate than the controls (P < 0.05); heifers assigned to Group c had a higher ovulation rate than those in Groups a or b (P < 0.05). More heifers assigned to Group c (7/17) superovulated than in the other 2 groups (P < 0.05). In conclusion, administration of 1.0 or 1.5 mg pFSH twice daily beginning at Day 3 of the estrous cycle in association with the induction of luteolysis increased the ovulation rate significantly when pFSH treatment was continued to onset of estrus. The ovulation rate and the occurrence of multiple ovulations were significantly higher when pFSH was administered at the time that the first dominant follicle was in decline.

The objective was to determine the effects of avoparcin, bovine somatotropin (bST) and the additive effects of both avoparcin and bST on milk yield, milk composition, live-weight changes and reproduction parameters in post partum dairy cows. Forty-eight autumn calving cows were allocated using a split-plot within randomized complete-block design to the following treatments: (i) control (2 mi saline plus 1 kg untreated concentrate per day); (ii) avoparcin (2 mi saline pills 1 kg concentrate containing 100 mg avoparin per day); (iii) bST (25 mg bST in 2 mi saline plus 1 kg untreated concentrate per day); and (iv) avoparcin plus bST (25 mg bST in 2 mi saline plus 1 kg concentrate containing 100 mg avoparcin per day)) All injections were given subcutaneously and treatment continued for 84 clays beginning 55 (s.e. 4) days after calving. The cows were offered grass silage ad libitum supplemented with 72 kg cereal-based concentrates daily. Milk yield and milk composition were measured thrice and once weekly, 1 espectively. The cows were weighed and body condition score was assessed every 2 weeks.Mean daily milk yield of cows assigned to control teas 20 1 (s.e. 1.5) kg, avoparcin, 21.5 (s.e. 1.5) kg, bST, 23.9 (s.e. 20) kg and avoparcin plus bST, 25.2 (s.e. 22) kg over the 84 days of the trial. bST increased milk yield proportionately by 0.18 compared ed with all cows not given bST (P < 0.01). Avoparcin did not significantly increase milk yield. There tons no effect of any treatment on milk composition, body weight or body condition score. None of the experimental treatments had any effect on calving to first service interval, calving to conception interval, number of services pel conception or overall conception rate.These results show that in early lactation, avoparcin alone had no effect on production or reproduction parameters in dairy cows; bST alone increased milk yield but did not affect any other production or reproduction parameter. There teas no significant additional increase in milk yield when avoparcin and bST were given in combination, compared with bST alone.

The objective of this study was to determine if alterations in dietary intake and(or) ovariectomy influence plasma concentrations of IGF-I, GH and LH in heifers. Cyclic heifers (n = 23) were individually fed for 10 wk either 1) 1.8% of body weight in dry matter per day (GAIN; n = 7) 2) 1.1% of body weight in dry matter per day (MAINT; n = 8); or 3) 0.7% of body weight in dry matter per day (LOSE; n = 8). After 10 wk of dietary treatment, heifers were ovariectomized 36 to 40 h following the second injection of prostaglandin F2α analog (2 injections 11 d apart). Heifers weighed 444 ± 13, 387 ± 8, and 349 ± 9 kg in the GAIN, MAINT and LOSE groups, respectively, at the time of ovariectomy; the average daily weight gains during the 10-wk period were 0.96, 0.17 and −0.31 kg, respectively (P < 0.001), for the 3 groups. Blood plasma was collected for 6 h at 15-min intervals 1 d before and 2 wk after ovariectomy. The MAINT group of heifers had greater IGF-I concentrations than either the LOSE or GAIN groups; IGF-I decreased (P < 0.05) by 23 and 35% after ovariectomy in the MAINT and GAIN groups, respectively, but did not change (P > 0.10) in the LOSE groups. Dietary restriction tended to increase (P < 0.10) GH pulse frequency and mean GH. Ovariectomy had no effect (P > 0.10) on mean GH or GH pulse frequency but increased (P < 0.05) GH pulse amplitude in the GAIN groups. Dietary treatment had no effect (P > 0.10) on mean LH, or LH pulse amplitude and frequency. However, across dietary treatments, ovariectomy increased mean LH and LH pulse frequency but did not affect (P > 0.10) LH pulse amplitude. In summary, dietary restriction increased GH secretion while ovariectomy increased LH secretion. There appears to be a dichotomy of response between GH and IGF-I in the way heifers respond to dietary treatment and(or) ovariectomy.

This experiment was conducted to evaluate the effect of bST on average daily gain, onset of puberty, first lactation milk yield, and reproductive efficiency in Friesian heifers.Heifers (n = 16 per treatment) were allocated to either: 1) control (1.5 ml of vehicle) or 2) bST (15 mg of bST in 1.5 ml of vehicle) using a randomized complete block design.Subcutaneous injections of bST were administered once daily from 7 mo of age for 120 d or until heifers reached puberty.Heifers were weighed every 2 wk. and blood samples were collected twice weekly after heifers reached 200 kg.Progesterone concentrations were used to determine onset of puberty.Heifers were bred between 16 and 18 mo of age and.following parturition, milk yield and composition were recorded twice weekly and once every 2 wk.respectively.Heifers assigned to bST treatment had an average daily gain (kg) of .8compared with .7 in control heifers.Number of days from birth to onset of puberty for bST-treated heifers was 401 compared with 381 for control heifers.Treatment with bST had no effect on milk yield, milk composition, or reproductive efficiency during the first lactation.These data demonstrate that daily administration of bST to Friesian heifers from 7 to 11 mo of age does not affect average daily gain, onset of puberty, reproductive efficiency, or first lactation milk yield of heifers.

The objective of this study was to determine if alterations in dietary intake of heifers can influence IGF-I concentrations in plasma and(or) follicular fluid (FFL), size of follicles, and steroid concentrations in FFL (as an indicator of steroidogenic capacity). Cyclic heifers [n = 23; mean +/- SE body weight (BW) = 373 +/- 7 kg] were individually fed for 10 weeks either: a) 1.8% of BW in dry matter (DM) per d (GAIN; n = 7), b) 1.1% of BW in DM per d (MAINT; n = 8) or c) 0.7% of BW in DM per d (LOSE; n = 8). After 10 wk of treatment, heifers were ovariectomized 36-40 hr after the second injection of prostaglandin F2 alpha analog (2 injections 11 d apart), and plasma and ovaries were collected. Heifers weighed 444 +/- 13,387 +/- 8 and 349 +/- 9 kg in the GAIN, MAINT and LOSE groups, respectively, at time of ovariectomy. Mean diameter of follicles greater than or equal to 10 mm was greater (P less than .05) for GAIN (15.6 mm) than for MAINT (11.0 mm) or LOSE (12.5 mm) heifers. Numbers of follicles and concentrations of IGF-I in plasma and FFL did not differ (P greater than .20) between LOSE, MAINT and GAIN heifers. Progesterone concentrations were greater (P less than .05) in small and medium follicles of GAIN than MAINT or LOSE heifers, but were unaffected by diet in large follicles. Estradiol concentrations in FFL in small, medium and large follicles were unaffected (P greater than .20) by dietary treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Friesian x Hereford heifers (n = 19; mean +/- s.e.m. body weight (BW) = 375 +/- 5 kg) were used in a randomized incomplete block design. Heifers were fed 0.7 (n = 7; L), 1.1 (n = 7; M) or 1.8% (n = 5; G) of BW in dry matter (DM)/day for 10 weeks. Ovaries were examined by ultrasound, for one oestrous cycle, from week 5 of treatment. Maximum diameter of dominant follicles was smaller (P less than 0.05) in L (11.8 +/- 0.1 mm) than in M (13.7 +/- 0.2 mm) or G (13.2 +/- 0.3 mm) heifers. Growth rate (mm/day) of dominant follicles during the oestrous cycle was not affected (P greater than 0.05) by dietary intake. Persistence of dominant follicles was shorter (P less than 0.05) in L (9.8 +/- 0.2 days) than in M (11.9 +/- 0.3 days) or G (12.7 +/- 0.4 days) heifers. Three dominant follicles were identified during the oestrous cycle of 5 of 7 L, 3 of 7 M and 1 of 5 G heifers (P less than 0.10); 2 dominant follicles were identified in the remaining heifers (n = 2 of 7, 4 of 7 and 4 of 5, respectively). Length of the luteal phase and luteal-phase concentrations of progesterone were not affected (P greater than 0.05) by treatment. Low dietary intake reduced the diameter and persistence of dominant follicles during the oestrous cycle of beef heifers and tended to increase the proportion of oestrous cycles with 3 dominant follicles.

The ovaries of 18 post-partum beef suckler cows were examined daily, using ultrasound, from Day 5 post partum until a normal oestrous cycle was completed. Periods of growth and regression of medium-sized (5-9 mm) follicles were identified before one medium follicle became dominant (single large follicle greater than or equal to 10 mm). The mean (+/- s.e.m.) number of days from parturition to detection of the first post-partum dominant follicle was 10.2 +/- 0.5. The first post-partum dominant follicle ovulated in 2/18 (11%) cows. The interval from calving to first ovulation (mean +/- s.e.m. = 35.9 +/- 3.3 days) was characterized by the growth and regression of a variable number (mean = 3.2 +/- 0.2; range 1-6) of dominant follicles. The maximum diameter of the dominant follicle increased as the cows approached first ovulation (P less than 0.05). Behavioural oestrus was not detected in 16/18 (89%) cows at first ovulation. Following first ovulation, the length of the subsequent cycle was short (mean = 9.7 +/- 0.5 days; range 8-15 days) in 14/18 (78%) cows and was characterized by the development and ovulation of a single dominant follicle. During oestrous cycles of normal length (mean = 20.6 +/- 0.5 days; range 18-23 days) one (N = 2), two (N = 7) or three (N = 8) dominant follicles were identified. The growth rate, maximum diameter or persistence of non-ovulatory dominant follicles before first ovulation or during oestrous cycles were not different (P greater than 0.05). These data show that, in beef suckler cows, follicular development and formation of a dominant follicle occur early after parturition and the incidence of ovulation of the first dominant follicle is low. The number of dominant follicles that develop before first ovulation is variable; first ovulation is rarely associated with oestrus and short cycles are common after first ovulation. It is concluded that prolonged anoestrus in post-partum beef suckler cows is due to lack of ovulation of a dominant follicle rather than delayed development of dominant follicles.