Body Condition Levels Research Articles

Relationship between energy status and fertility in Czech Fleckvieh cows

The aim of this study was to confirm that a negative energy balance expressed by declining body condition score (BCS) can lead to the deterioration of fertility results of Czech Fleckvieh cows. The BCS of cows was evaluated before calving and during the first five weeks of lactation. The evaluation was based on 338 Czech Fleckvieh cows calved between the October 13th, 2009 and April 27th, 2010 at one dairy farm. Analysis of relationships between the energy balance results and fertility score expressed by the reproduction results (pregnancy rate after the first and all inseminations, the insemination interval, service period, insemination index, calving period) of the observed group were performed. The higher body condition score of the Czech Fleckvieh cows before calving turned out advantageously regarding the energy source during the postpartal period. No negative effect of higher BCS in cows before calving was confirmed. The best reproduction parameters were attained in the group of cows with no change or marked increase of body condition after calving recorded. However, statistically significant differences between the groups were detected only in the third week of lactation. Significant differences in the level of body condition were detected in relation to the length and type of oestrus onset.

Relationships among body condition score, milk yield and reproduction in Czech Fleckvieh cows

The objective of this study was to confirm the relationship among body condition score at the time around parturition, milk yield in subsequent lactation, reproductive efficiency and BCS development in Czech Fleckvieh dairy cows. The BCS and milk yield were measured once a month and the cows were divided into groups according to their BCS before and after calving. Next, data from the database of cattle reproduction of the Czech Fleckvieh herd book were used. The dataset was analyzed by multifactorial analysis of variance using procedures COOR and GLM of the statistical program SAS. Cows with lower BCS in the 1<sup>st</sup> month after calving showed an increase in both milk yield and fat and protein corrected milk (FPCM) yield. No significant relationship was found between the BCS level before calving and subsequent milk yield. The body condition level in the last month before parturition influenced its subsequent decrease in the first phase of lactation. The group of cows with the highest BCS level before calving retained a high BCS level in the first five months of lactation. Adequately, the group of cows with the lowest BCS in the first month of lactation had the lowest BCS in the next four months. BCS before calving was not related to reproduction indicators, but the significant effect of BCS in the 1<sup>st</sup> month after calving on the length of calving to the first service interval was confirmed. The group of cows with BCS > 3.5 in the 1<sup>st</sup> month after calving had the most favourable reproduction indicators, also when the milk yield level was taken into account.

Potential for Estimation of Body Condition Scores in Dairy Cattle from Digital Images

Body condition scoring, an indirect measure of the level of subcutaneous fat in dairy cattle, has been widely adopted for research and field assessment or for management purposes on farms. The feasibility of utilizing digital images to determine body condition score (BCS) was assessed for lactating dairy cows at the Scottish Agricultural College Crichton Royal Farm. Two measures of BCS were obtained by using the primary systems utilized in the United Kingdom (UK-BCS) and the United States (USBCS). Means were 2.12 (±0.35) and 2.89 (±0.40), modes were 2.25 and 2.75, and ranges were 1.0 to 3.5 and 1.5 to 4.5 for the UKBCS (n=2,346) and USBCS (n=2,571), respectively. Up to 23 anatomical points were manually identified on images captured automatically as cows passed through a weigh station. Points around the hooks were easier to identify on images than points around pins and the tailhead. All identifiable points were used to define and formulate measures describing the cow's contour. For both BCS systems, hook angle, posterior hook angle, and tailhead depression were significant predictors of BCS. When the full data set testing only the angles around the hooks was used, 100% of predicted BCS were within 0.50 points of actual USBCS and 92.79% were within 0.25 points; and 99.87% of predicted BCS were within 0.50 points of actual UKBCS and 89.95% were within 0.25 points. In a reduced data set considering only observations in which the tailhead depression angle was available, adding the tailhead depression to models did not improve model predictions. The relationships of the calculated angles with USBCS were stronger than those with UKBCS. This research demonstrates the potential for using digital images for assessing BCS. Future efforts should explore ways to automate this process by using a larger number of animals to predict scores accurately for cows across all levels of body condition.

Effects of level of food intake on ovarian follicle number, size and steroidogenic capacity in the ewe.

The effect of high (H) or low (L) levels of food intake, during the preceding 4 weeks, on ovarian follicle numbers and steroidogenic capacity were investigated in groups of 12 adult Scottish Blackface ewes. Ewes of the two treatments had similar levels of body condition at the time of study but there was a twofold difference in levels of food intake. Ovaries were surgically removed on day 11 or 12 of the oestrous cycle (luteal phase; n = 6 per nutritional treatment) or at 30 h after injection (i.m.) of prostaglandin F2alpha analogue on day 11 or 12 of the cycle (follicular phase; n = 6 per nutritional treatment). Ovarian follicles > 1 mm diameter were dissected out and incubated individually for 2 h at 37 degrees C, in 1 ml of medium 199 which was then assayed to determine concentrations of oestradiol and testosterone. There were significantly more small follicles (1-2.5 mm diameter) in (H) than (L) ewes (P < 0.05) but no treatment difference in the numbers of large follicles (> 2.5 mm diameter) during either phase of the cycle and no difference in the mean diameters (mm) of the two largest follicles in each animal. However, although there were higher rates of synthesis of both oestrogen (P < 0.05) and testosterone (P < 0.01) in the large follicles of (L) ewes as compared with (H) ewes, there was a lower oestrogen/testosterone ratio in (L) than (H) follicles which may indicate a lower level of aromatase activity in (L) follicles. It is concluded that the effects of level of food intake on ovulation rate are expressed through differences in late stages of follicle development, probably through effects on the intrafollicular steroid milieux.

Effects of infusion of GnRH pulses and level of body condition on ovarian function in postpartum beef cows

An experiment was conducted to test the hypothesis that postpartum anoestrus in beef cows is prolonged in cows in low body condition (BC) because they have a reduced LH pulse frequency compared with cows in high BC. Thirty-six multiparous Blue-Grey (White Shorthorn × Galloway) cows were fed so that they calved in either low (L) (BC score 2.07; SE 0.05; n = 24) or high (H) (BC score 2.81; SE 0.08; n = 12) body condition. They were then fed to maintain BC after calving. Twelve L cows were infused (i.v.) with 2 μg GnRH in 2 ml saline every 2 h from 5 to 7 weeks postpartum (LG) while the remaining L cows and all H cows were infused with saline only (LS and HS). Ovulations, as indicated by the presence of a morphologically normal corpus luteum, were recorded in one, one and ten of the cows of the LS, HS and LG groups, respectively. Mean LH concentrations and pulse frequencies were not affected by either GnRH treatment or BC but mean LH pulse amplitudes were lower ( P < 0.05) in LG and LS cows than in HS cows at Week 5 and in LG cows at Week 6. At Week 7 postpartum, the numbers of small (3–7.9 mm diameter) and large (≥ 8 mm diameter) ovarian follicles, mean granulosa cell numbers per follicle and mean concentrations of LH receptors (pg per mg thecal and granulosa tissue) were not affected by GnRH treatment or BC. Granulosa cells from oestrogen active follicles of HS and LG cows secreted more oestradiol in vitro ( P < 0.01) than cells from LS cows. However, there were no significant differences with treatment in the intrafollicular concentrations of oestradiol, testosterone or insulin-like growth factor-1. It was concluded that, since infusion of GnRH pulses enhanced both follicular steroidogenesis and the incidence of ovulation in low BC cows, the frequency of GnRH pulses is one determinant of follicle development in the postpartum cow. While H cows also exhibited a degree of enhancement of oestradiol synthesis by the granulosa cells of oestrogenic follicles, compared with L cows there was no difference in the LH pulse frequency or in the incidence of ovulation. It is concluded that there may be a threshold level of oestrogen synthesis by granulosa cells below which the final stages of follicle maturation and ovulation cannot be initiated, or that a high rate of oestradiol synthesis by this tissue is not the only factor mediating the effects of body condition on follicle development in the postpartum cow.

Naloxone evokes a nutritionally dependent LH response in post partum beef cows but not in mid-luteal phase maiden heifers

AbstractData from two experiments are reported which test the hypothesis that nutrient and/or dry-matter intake and body condition may interact to modify hypothalamic opioidergic activity and thus influence the pulsatile release of LH during the early post-partum period and during the oestrous cycle. Experiment 1 involved 16 multiparous, twin-suckling beef cows, and was a 2 × 2 × 2 factorial design in which the factors were level of post-partum energy intake (80 v. 130 M) metabolizable energy (ME) per day), the digestible undegradable protein (DUP) content of the post-partum diet (14 v. 31 g/kg dry matter), and treatment with either 200 mg or 400 mg naloxone hydrochloride. Blood samples were collected at 15-min intervals for 4h at weeks 4 and 7 post partum. Naloxone was administered intravenously after the eighth sample. Experiment 2 involved 16 cyclic maiden heifers and was also arranged in a factorial manner, with two levels of body condition at the start of the experimental period (2·50 and 3·16 units) and two levels of energy intake thereafter (40 and 80 MJ ME per day). Seven blood samples were collected at 15-min intervals on 4 days consecutively during the mid-luteal phase of the oestrous cycle. On the first 2 of these 4 days naloxone was administered, whilst on the last 2 days a gonadotropin-releasing hormone agonist (buserelin; GnRH) was administered, both after the fourth sample. Plasma from both experiments was assayed for LH and prolactin (Prl).In experiment 1, cows on 130 MJ ME per day returned to oestrus and ovulated earlier than cows on 80 MJ ME per day (44·5 v. 55·0 days; s.e.d. = 3·93; P &lt; 0·05). At week 4 post partum the proportional increase in plasma LH following naloxone challenge was greater for cows on 130 MJ ME per day than cows on 80 MJ ME per day (1·38 v. 1·12; P &lt; 0·05), but the converse was true at week 7 (1·15 v. 1·68; P &lt; 0·05). Cows on the high DUP diet required a higher dose of naloxone to elicit an LH response. Few heifers in experiment 2 exhibited an LH response to naloxone. In contrast, there were significant dietary treatment effects on the LH response to GnRH (P &lt; 0·01). Relatively thin heifers on 40 MJ ME per day exhibited the lowest proportional increases in plasma LH to GnRH challenge, whereas heifers on 80 MJ ME per day and given the higher dose of GnRH produced the greatest plasma LH responses. Mean Prl concentrations before and after feeding in experiment 2 were respectively 13·2 and 10·2 ng/l (P &lt; 0·01).Suckled cows given a high energy diet during the early post-partum period can overcome the opioid mediated block on LH release and resume oestrous cycles earlier than cows given a low energy diet. LH would appear to be inhibited by a non-opioid mechanism in mid-luteal phase heifers. Total pituitary reserves ofLH may be influenced by the animals nutritional status.

Oestrous Activity and Ovulation Rate in Rasa Aragonesa Ewes Maintained at two Different Body Condition Levels Implanted or Reimplanted in the Seasonal Anoestrus with Exogenous Melatonin

The effects of melatonin implants in advancing the breeding season and enhancing both ovulation rate (OR) and litter size in the ewe are well documented (Haresign et al., 1990; López and Inskeep, 1991). Likewise, oestrous activity and OR in the early breeding season can be stimulated by a moderately and constant body condition (BC) in Mediterranean sheep breeds (Forcada et al., 1992). However, little information is available in relation to the effect of nutritional status in ewes receiving exogenous melatonin on reproductive parameters. The present study was carried out to determine the effects of a constant BC throughout the year, and implant or reimplant of exogenous melatonin on onset of oestrous activity and OR in a reduced seasonality sheep breed.The experiment was designed as a 2x2 factorial. Factors were two constant BC levels (≤2.50; L, and ≥2.75; H) and two forms of melatonin treatment (one implant -Melovine™- placed the 8th April; M, and a second implant 49 days later; 2M).

Seasonal changes in oestrus activity and ovulation rate in Rasa Aragonesa ewes maintained at two different body condition levels

Onset and duration of seasonal anoestrus and seasonal changes in ovulation rate were studied for two consecutive years in two groups of Spanish Rasa Aragonesa ewes with body condition (BC) scores ⩽ 2.5 (low BC group) or ⩾ 2.75 (high BC group). Animals were kept penned throughout the experiments (November 1987–September 1988 and February–September 1989) (latitude 41° 40′N). Mean liveweights and BC were similar at the beginning and end of both study periods. Oestrus was tested daily using aproned males. Ovulation rate was measured by laparoscopy 6 d after identification of oestrus. Animals were blood sampled for progesterone determination every 6 d during the 1989 experiment. The high BC group of ewes showed a shorter seasonal anoestrus than the low BC group in both study years (64 vs. 113 and 76 vs. 92 d in 1988 and 1989) ( P < 0.05). Differences in percentage of detected oestrus between groups were found in the transition periods between breeding seasons and seasonal anoestrus, and vice versa; and were higher in 1988 (74 vs. 34% in April, and 92 vs. 50% in July) ( P < 0.01) than in 1989 (50 vs. 21% in April) ( P < 0.05). Plasma progesterone concentrations showed a great number of ovulations were unaccompanied by oestrus, specially in the anoestrus period, ranging between 10.8–46.4% in May/June cycles. There was a marked seasonal change in ovulation rate. For the low BC group, the ovulation rates were consistently lower than those of the high BC group in both years, especially in September (1.25 vs. 1.67 and 1.09 vs. 1.67 corpora lutea in 1988 and 1989) ( P < 0.001). Ewes with lower body fat reserves less effectively reactivated their ovulation potential in the first cycles of each new breeding season.

Effects of body condition at calving and feeding level after calving on LH profiles and the duration of the post-partum anoestrous period in beef cows

AbstractAn 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 × 2 factorial experiment. At calving, mean body condition scores were 2·85 (F) and 2·23 (T) (P &lt; 0·001) while live weights were 521 kg and 457 kg (P &lt; 0·001) for F and T cows respectively. After calving metabolizable energy intakes were 111 and 118 MJ/day (H) or 56 and 64 MJ/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 &lt; 0·001). The number of cows still acyclic on 1 May each year was higher (P &lt; 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 &lt; 0·01) but not in the F cows (80 v.89 days for the FH and FL cows respectively; P &gt; 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.

FSH and LH receptor concentrations in large ovarian follicles of beef cows in high and low levels of body condition at nine weeks post partum.

An experiment was conducted to determine whether or not the effect of body condition at parturition, and thereafter, on the duration of the post-partum anoestrous period was mediated through differences in gonadotrophin receptor concentrations in the ovarian follicles. Two groups of cows were fed to achieve body condition scores of > or = 2.75 (H; n = 14) or < or = 2.00 (L; n = 15) at parturition (this had led to differences in the duration of post-partum anoestrus in previous experiments) and then fed to maintain liveweight and condition until ovariectomy at nine weeks post partum. There was no effect of body condition on the mean (+/- s.e.) number of large (> or = 8 mm diameter) follicles per cow (3.0 +/- 0.27) but a greater proportion of the follicles of H cows, compared with L cows, was oestrogenic (secreting > 250 pg oestradiol h-1 in culture) (0.75 v. 0.5; chi 2 = 3.40; P = 0.06). Mean concentrations (pg hormone bound per mg protein) of follicle stimulating hormone (FSH) receptors in both granulosa (H, 157.3; L, 136.6; standard error of difference (s.e.d.) = 27.2) and thecal tissue (H, 4.14; L, 4.35; s.e.d. = 1.66) were similar for H and L cows. There was no difference associated with treatment in luteinizing hormone (LH) receptor concentrations in either granulosa (H, 40.3; L, 37.2; s.e.d. = 6.67) or thecal tissue (H, 48.9; L, 48.0; s.e.d. = 6.03). The concentration of FSH receptors in granulosa tissue was lower in non-oestrogenic follicles than in oestrogenic follicles (80.0 v. 188.1; s.e.d. = 40.4; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of body condition on ovarian sensitivity to exogenous FSH in ewes in which endogenous gonadotrophin secretion is suppressed

The results of previous experiments indicate that the effect of body condition (BC) on ovulation rate is mediated through changes in the number of large, potentially ovulatory, ovarian follicles. However, these differences in follicle populations were not associated with consistent differences in gonadotrophin profiles. It was therefore postulated that effects of level of BC on follicle development and ovulation rate are due to differential ovarian sensitivity of FSH.Two groups of 20 Scottish Blackface ewes were fed differentially so that they achieved mean (±s.e.m.) body condition scores of 1.78±0.017 (Low; L) and 2.94±0.031 (High; H) by 2 weeks before sample collection. They were then fed to maintain these body conditions throughout the remainder of the experiment. Four weeks before study, Alzet minipumps (Charles Rivers UK Ltd.) containing GnRH agonist (buserilin; Hoechst AG; Frankfurt, F.R.G.) were inserted, subcutaneously, in all ewes. This treatment partially suppresses FSH secretion and totally inhibits LH pulses so that growth of ovarian follicles &gt;2.5 mm in diameter is inhibited.

The effect of level of nutrition prior to mating on the reproductive performance of ewes of two welsh breeds in different levels of body condition

ABSTRACTThe effects of high-low (HL) and low-high (LH) patterns of nutrition during the 5 weeks prior to a synchronized mating were studied on the reproductive performance of 115 Welsh Mountain and 114 Brecknock Cheviot ewes in a range of body condition at the start of treatment. For 2 months prior to treatment imposition, ewes were grazed in a systematic way at different stocking rates on different sward heights to obtain a range of body condition scores. Target score groupings were 2·00 to 2·25, 2·50 to 2·75 and 3·00 to 3·25 and although scores of 1·50 to 3·25 were obtained, most lay in the 2·00 to 2·75 range. Two treatment groups, balanced for live weight and body condition score, received high and low levels of nutrition for 16 days from mid October, achieved, respectively, by a low stocking rate on a sward with a high surface height plus ad libitum concentrate and a high stocking rate on a sward with a low surface height plus 200 g hay per head per day. Treatments were then reversed for the 17 days prior to mating. Live-weight and body condition-score changes were recorded and reproductive performance at first mating was measured from counts of corpora lutea and viable embryos at slaughter either at return to service or at 4 weeks after first mating. There were no differences due to nutritional pattern in live weight or body condition score at mating. The LH treatment significantly increased the rates of ovulation, conception, multiple ova survival and potential lambing per ewe pregnant and per ewe mated in the Welsh Mountain breed but significantly increased only the rates of ovulation and potential lambing per ewe pregnant in the Brecknock Cheviot breed compared with the HL treatment. The relatively poorer response in the latter breed was partially due to a lower ovulation rate potential coupled with non-significantly lower rates of conception and survival of single-shed ova associated with the LH treatment. Much of this relatively poorer reproductive performance in the Brecknock Cheviot breed was in ewes with body condition scores 3= 2·75. Reproductive performance increased with increasing body condition at the start of treatment over the range of scores =≤ 2·25 to 2·50 in both breeds and, while continuing to improve in scores above 2·50 in the Welsh Mountain breed, in the Brecknock Cheviot breed it started to decline. Ewes with a body condition score of 2·50 in both breeds showed the greatest response in potential lambing rate to the LH treatment.

Pre-mating herbage intake and the reproductive performance of north Country Cheviot ewes in different levels of body condition

ABSTRACTOver 4 years, a flock of mature North Country Cheviot ewes was grazed on different swards between weaning in August and mid October to achieve a range of condition scores at 5 weeks before mating (post-weaning period). During the subsequent 5 weeks before a synchronized mating (pre-mating period), all ewes were grazed on a perennial ryegrass/white clover sward, provided at high (H) or low (L) herbage masses (1600 to 2100 or 1200 to 1400 kg dry matter (DM) per ha, respectively). Ovulation rate was derived from the number of corpora lutea in 101 ewes slaughtered after first mating. Conception and lambing rates were derived from the number of lambs born to first mating of 406 ewes. In 2 out of the 4 years, 79 ewes were used to estimate herbage intake.There was no effect of post-weaning management on reproductive performance. Herbage intake and reproductive performance were examined in relation to the body condition of the ewes at 5 weeks before mating. On an H herbage mass pre-mating, herbage intake in the period immediately prior to mating was greatest in ewes in low body condition and declined significantly with increasing condition. On an L herbage mass pre-mating, herbage intake did not vary significantly with condition. Ovulation rate was low in ewes in low body condition (scores =≤·25) at 5 weeks before mating, increased significantly with increasing condition up to scores 2·50/2·75 but did not change significantly above such intermediate scores. Conception and lambing rates increased significantly with increasing body condition up to scores 2·50/2·75 and then decreased significantly as condition increased above these levels. These effects of body condition were greater on an L herbage mass pre-mating than they were on an H herbage mass. Ewes in the intermediate body condition scores of 2·50 and 2·75 at 5 weeks before mating had a low sensitivity to contemporary nutrition pre-mating. Such condition levels are therefore considered to be above the range of condition in the North Country Cheviot breed within which reproductive response is affected by contemporary nutrition pre-mating.The lower reproductive performance of ewes in high body condition (scores 3=3·00) at 5 weeks before mating was related to an increase in estimated ova and embryo loss and may be associated with a reduced herbage intake.

Ovarian follicle populations, steroidogenicity and micromorphology at 5 and 9 weeks post partum in beef cows in two levels of body condition

ABSTRACTThe effect of body condition at calving on ovarian follicle characteristics during post-partum anoestrus was studied in 38 suckling Blue-Grey cows with mean body-condition scores of 2·80 (s.e. 0·05) (H) or 2·35 (s.e. 0·05) (L) at calving and fed so that they maintained live weight and body condition during lactation. Cows of each level of body condition were ovariectomized at either 5 or 9 weeks after calving and follicles ≥3 mm in diameter were dissected out and incubated in a medium (Medium 199) for 2 h. Follicle incubates were assayed for progesterone, testosterone and oestradiol. L cows had fewer follicles ≥3 mm in diameter than H cows (24·1 v. 44·9; P &lt; 0·05) at 5 weeks post partum due to a lower number of small (3 to 4 mm) follicles (12·9 v. 30·6; P &lt; 0·05). At 9 weeks there was no effect of body condition on mean numbers of follicles (38·1 v. 40·4; P &gt; 0·05). The proportions of healthy, intermediate and atretic follicles in all cows were 0·35, 0·20 and 0·45 respectively; these proportions were not affected by body condition or time of ovariectomy. Body condition did not affect the overall mean capacity of the cultured follicles to produce oestradiol or progesterone in vitro but testosterone production was higher in follicles from H than L cows (6406 v. 5206 pg/h; P &lt; 0·05). However, at 9 weeks post partum a greater proportion of H than L cows had a large (&gt;8 mm), healthy, highly oestrogenic follicle (4/8 v. 1/7; P = 0·18).At 9 weeks post partum, the four large, healthy, oestrogen-active follicles (those secreting &gt;250 pg/h) from H cows were approximately 11-fold more oestrogenic than the single comparable follicle from L cows (7100 v. 635 pg/h; P &gt; 0·05). There was little difference at week 5 post partum: 3288 and 2785 pg/h (P &gt; 0·05) for H and L cows respectively. Oestrogen-active follicles from H cows were significantly more oestrogenic at 9 than 5 weeks post partum (5807 v. 3021 pg/h; P &lt; 0·05). The results suggest that the body condition-related reduction in the number and steroidogenic capacity of large oestrogenic follicles in post-partum cows may be associated with a reduction in LH pulsatility.

Circulating concentrations of LH and FSH and pituitary responsiveness to GnRH in intact and ovariectomized suckled beef cows in two levels of body condition

ABSTRACTThe 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 &lt; 0·05) and 15 days after ovariectomy (0·86 v. 0·72 pulses per h; P &lt; 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 &lt; 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.

The effect of different pasture management strategies during the weaning-to-mating period on reproductive performance of Greyface ewes

ABSTRACTThe effects on reproductive performance of different strategies of pasture management designed to conserve herbage in situ during the late growing season for use during the pre-mating and mating period were studied in three experiments over 3 years with Greyface ewes. Two experiments with 341 ewes compared set-stocking of pasture at 12 ewes per ha on two initial levels of herbage mass with a conservation strategy which left half of the area ungrazed and grazed the other half of the area at 24 ewes per ha from late August until mid October (2 weeks before the start of mating) after which the total area was grazed at 12 ewes per ha. In a third experiment with 124 ewes, the conservation strategy left a quarter of the area ungrazed and varied stocking rate to a minimum of 12 ewes per ha to maintain two initial levels of herbage mass on the other three-quarters of the area and then compared set-stocking at six ewes per ha on this area with set-stocking at 18 ewes per ha on the previously ungrazed quarter of the area during the pre-mating and mating period.Initial levels of herbage mass were within the range of 2000 to 2100 kg dry matter (DM) per ha (7 cm sward height; high) and 1500 to 1700 kg DM per ha (4 to 5 cm; low). Mean herbage accumulation rates between August and October were estimated to be 25 and 44 kg DM per ha per day in the first two experiments. Initial live weight and body condition score also varied considerably between years and subsequent response was influenced by herbage growth rate. Where mean ewe body condition was within the score 2·75 to 3·00, range over the mating period and herbage mass on set-stocked areas was not higher than 2200 kg DM per ha (8 cm sward height) in the pre-mating period or not lower than 1300 kg DM per ha (3·5 cm) at about 3 weeks after mating, the strategy of management did not influence reproductive performance in terms of the number of lambs born. Within these limits, however, reproductive performance was positively related to herbage mass in late August (low = 1·60, high = 1·94).When herbage mass fell below the 1300 kg DM per ha level before or during mating, reproductive performance was improved by a herbage-conservation strategy which maintained ewe body-condition score within the 2·75 to 3·00 range. When herbage mass and growth rate were high, reproductive performance was also improved by a herbage-conservation strategy which restricted the development of excessive body condition before mating by avoiding the increase in barrenness shown to derive from very high levels of body condition.

Effect of level of food intake on hypothalamo-pituitary sensitivity to ovarian Steroid feedback in ewes

Effects of level of food intake and body condition on ewe hormone status, ovulation rate and reproductive performance may be mediated either through a direct effect on hypothalamic or pituitary activity or through an indirect effect on the sensitivity of either or both of these organs to steroid feedback. The aim of this experiment was to determine the effect of level of food intake of ewes on hypothalamic activity and pituitary responsiveness to gonadotrophin-releasing hormone (GnRH) in the presence of ovarian steroids. Sensitivity to steroid feedback cannot be measured in an entire animal, owing to the variable and irregular nature of ovarian steroid secretion. Ovariectomised ewes were therefore used together with steroid replacement therapy.Two groups of 16 ewes were fed to achieve body condition scores of either 2.00 or 2.25/2.50 by 3 weeks before the period of study. Thereafter, ewes of the lower condition score were fed dried grass pellets ad libitum and 250 g hay/head/day (H) while those of the higher condition score were fed 1050 g pellets and 250 g hay/head/day (M), a ration designed to maintain liveweight and condition score so that at the time of study, ewes of the two groups had a similar level of body condition but different levels of intake.

Relationship between body condition and levels of serum luteinizing hormone in postpartum mares

To study the endocrine environment of foaling mares at different levels of body condition, 12 mares were divided equally into two groups, one designed to foal at a condition score of 4.5 or less (thin) and the other to maintain a condition score of 6 or greater (control). Serum samples were collected twice weekly before foaling, and daily thereafter until 7 d following the second estrous cycle after parturition. Serum levels of luteinizing hormone (LH) were measured by Radioimmunoassay. In addition, mares were weighed, body condition was scored and body fat content was measured weekly. One consequence of low body condition at foaling in thin mares was a longer mean gestation length than in control mares. Also, the pattern of LH observed during the first and second estrous cycles after foaling was different for thin vs control mares. Serum LH concentrations for thin mares were greater during their second estrous cycle than during their first estrous cycle. Also, in thin mares, the interval from parturition to ovulation, as indicated by the day of maximum concentration of LH during estrus, was random. Control mares had equivalent concentrations of serum LH in both cycles, and they had predictable intervals from parturition to ovulation. LH patterns in thin mares were similar to those reported in mares during seasonal transition, whereas LH patterns of control mares were similar to those reported in mares during the middle of the breeding season.

Effect of level of food intake at mating on the reproductive performance of ewes passively immunized against testosterone

AbstractIn a 2 × 2 × 2 experiment, 296 Scottish Blackface ewes were fed to achieve one of two levels of body condition (high: condition scores ^2·75; low: condition scores ^2·50) by 2 weeks before joining with rams. Half of the ewes of each condition score were fed dried grass pellets ad libitum and 300 g hay per head daily, between 2 weeks before and 8 days after joining, while the remaining ewes were offered a live-weight maintenance ration comprising 750 g pellets and 400 g hay per head daily. From 8 days after joining the intake of all ewes was gradually changed, over a 2-week period, to 1250 g pellets and 400 g hay per head daily. Two days before joining, half of the ewes of each condition/intake group were passively immunized against testosterone. A total of 99 ewes were slaughtered 18 days after joining and their ovulation rate at the first mating determined. Ovulation rates were significantly affected by immunization (immunized: 2·31, control: 1·86, pooled s.e. = 0·055; P &lt; 0·01) and food intake (ad libitum: 2·24, maintenance: I 92, pooled s.e. = 0·055; P &lt; 0·05) but not by body condition at mating (high: 2·15, low: 2·02, pooled s.e. = 0·059; P &gt; 0·05). Lambing rates were dependent on treatment (immunized: 1·82 control: 1·62, pooled s.e. = 0·044; P &lt; 0·01), food intake (ad libitum: 1·85, maintenance: 1·59, pooled s.e. = 0·043; P &lt; 0·01) and body condition (high: 1·82, low: 1·62, pooled s.e. = 0·044; P &lt; 001). In ewes in a high body condition at mating, the effects of intake and immunization were additive but in ewes in low condition, immunization induced little improvement in performance in ewes fed ad libitum. Circulating antibody titres were lower in ewes fed ad libitum than in ewes offered a maintenance ration (1: 416 v. 1: 534, pooled s.e. = 14; P &lt; 0·001), but ovulation rates and litter sizes were not related to titres.

Effect of level of food intake on the reproductive performance of ewes in different levels of body condition at mating, following passive immunisation against testosterone

In a 2 x 2 x 2 experiment, 296 Scottish Blackface ewes were fed to achieve one of 2 levels of body condition (high : C.S. ⩾ 2.75; low : C.S. ⩽ 2.50). Half of the ewes of each condition group were then fed dried grass pellets ad libitum with 300 g hay/ head/day (high intake); the remainder were fed a liveweight maintenance ration of 750 g pellets and 400 g hay/head/day (low intake) between 14 days before and 8 days after joining. Thereafter, feed levels for both groups were gradually adjusted to 1250 g pellets and 400 g hay/head/day which was fed until mid pregnancy after which they were fed according to foetal load. Mean daily inatkes of dried grass pellets for ewes fed ad libitum were 2.45 and 2.27 kg fresh weight/head/day for ewes in the low and high condition groups respectively. The patterns of liveweight and condition score changes associated with these feeding regimes are summarised in Table 1.