Effect of temporary weaning and creep feeding on calf growth and the reproductive efficiency of their Hereford dams.

OBJECTIVE: The objective was to test if creep feeding (CF) improves the average daily gain (ADG) and weaning weight of calves submitted to temporary weaning (TW) and if the combination of CF and TW improves conception and pregnancy rates of cows. METHODS: Primiparous (n = 74) and primiparous and multiparous (n = 104) cows grazing native grasslands were used in experiment 1 and 2; respectively. The experimental design was in plots divided into complete random blocks with two replications. The CF was the big plot and TW the small plot, thus four experimental groups were formed: i) -CF-TW (n = 21 and 27); ii) -CF+TW (n = 16 and 24); iii) +CF-TW (n = 20 and 26); iv) +CF+TW (n = 17 and 27) with cow-calf pairs for experiments 1 and 2; respectively. Nose plate application for TW had a duration of 14 and 15 days for experiment 1 and 2: respectively. In experiment 1, calves were fed at 1% of live weight for 112 days using a commercial supplement with 18.4% crude protein. In experiment 2, the supplementation lasted 98 days, and was carried out with corn dried distillers grains with soluble (DDGS) at 40% of the potential intake on a daily basis. RESULTS: The TW reduced ADG during the TW period and the following 14 days, but the negative effect of TW was maintained until the final weaning only in experiment 2. The CF increased ADG during TW period in both experiments. The TW promoted an earlier conception of the dams (12 days in -CF treatment and 19 days in +CF treatment, p<0.01) and CF increased pregnancy rate in experiment 1, being the effects not consistent between experiments. CONCLUSION: The CF consistently promoted an increase in ADG during the period of TW and increased final weaning weight of calves, therefore it is economically viable.

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Antral follicular count is a tool that may allow the selection of more precocious Bradford heifers at weaning.

Although antral follicle count is a repeatable parameter across life that is positively associated with fertility, its use at weaning as a tool to discard less fertile heifers has not been extensively evaluated. The hypotheses of this work are: 1) maximum antral follicle count (MAFC) is repeatable between weaning and pre breeding evaluations, allowing selection of more fertile heifers at an early age, 2) heifers with high MAFC have growth and development parameters linked to an earlier puberty and pregnancy, 3) MAFC has a positive correlation with AMH concentrations, so that both could be used inter changeably. In this study, Hereford (n = 42 and n = 50) and Braford (n = 40 and n = 50) females were used in years 1 and 2; respectively, in a completely randomized experimental design. Heifers were examined for five to ten days at two different moments (post weaning and pre service), to determine MAFC. The concentrations of Anti müllerian hormone (AMH) were evaluated on the day of MAFC assessment. Growth and development parameters were evaluated post weaning and pre service. The repeatability of MAFC between post weaning and pre service evaluations was poor in three cases (Hereford Year 1 = 0.36 and 2 = 0.39 and Braford, Year 2 = 0.32) but it was high for Braford in Year 2 (0.72). The AMH repeatability between post weaning and pre service evaluations was high in one case (Braford Year 2 = 0.72) and moderate in the others (Year 1, Hereford = 0.50 and Braford = 0.52 and Year 2, Hereford = 0.50). In Year 2, Braford heifers with greater MAFC attained puberty at an earlier age (r2 = 0.129; P = 0.0196). Also, diminished MAFC corresponded with decreased growth and development, thus less Braford heifers with low MAFC were inseminated (2/16), compared to those with medium (12/17) and high MAFC (7/17; P < 0.01). Moreover, Braford heifers with low AFC had less progesterone in the cycle post insemination but pregnancy rate was not affected. In Braford heifers in Year 2, there was a high correlation between MAFC and AMH concentrations (0.85 P < 0.001). The results of these experiments indicate that post weaning MAFC and AMH concentrations may be applied to select those Braford heifers that attain puberty at an early age, but these tools are not useful in Hereford heifers.

Long-term effect of early nutrition on endocrine parameters and liver and endometrial gene expression of the members of the somatotrophic axis in Hereford heifers.

This study compared the effect of different management systems on endocrine parameters, and gene expression of members of the somatotrophic axis in the liver and endometrium of beef heifers. Twenty-two 709-days-old heifers submitted to Early Weaning (EW, n = 8), Traditional Weaning (TW, n = 7) and TW plus creep feeding (TW+CF, n = 7) were used. Animals were synchronized with two prostaglandin (PG) injections at 11-day interval (Oestrus = Day 0). Blood samples were collected daily for progesterone (P4) determination, and endometrial and liver biopsies on Days 7 and 16 for transcript determination of members of the somatotrophic axis. Progesterone concentrations were greater on Days 15 and 16 (p < .02) of the cycle in TW+CF than TW and EW heifers. On Day 7, TW+CF heifers expressed greater liver total growth hormone receptor transcripts than TW heifers (p = .05) and greater insulin-like growth factor (IGF)-binding protein 3 mRNA than both EW and TW groups (p < .05). On Days 7 and 16, TW+CF expressed more endometrial IGF1 mRNA than the other groups (p < .01). We conclude that increasing the plane of nutrition of nursing calves may have a long-term effect on the functioning of the somatotrophic axis both in the liver and in the endometrium.

Short term protein supplementation during a long interval prostaglandin-based protocol for timed AI in sheep.

The aim of this study was to evaluate the reproductive impact of a short-term protein supplementation on a long interval prostaglandin-based protocol (two PG injections 15 d apart; PG15) for timed artificial insemination in sheep. During the breeding season, 437 multiparous Merino ewes grazing native pastures (forage allowance of 6 kg of dry matter/100 kg of live weight; crude protein: 10.8%, metabolic energy: 2.1 Mcal/kg of dry matter) were selected. Ewes were allocated, according to body condition score (3.2 ± 0.2) and body weight (40.6 ± 4.9 kg, mean ± SD), to a 2 × 2 factorial design: type of estrus -spontaneous estrus (SE) or induced with PG15 (PG15)-, and supplementation (yes or no) before insemination (+FF; soybean meal at Days -10 to -3; crude protein: 51.9%, metabolic energy: 2.8 Mcal/kg of dry matter; average consumption 0.9% live weight/ewe/day of dry matter). All ewes were cervically artificial inseminated (Day -2 to -3 in SE ewes at estrus detection; Day 0 = timed artificial insemination in PG15 ewes). Ovulation rate on Day 7, non-return to service on Day 23, conception, fertility, prolificacy and fecundity on Day 60 were evaluated. Ovulation rate (1.17 ± 0.40 vs. 1.06 ± 0.25), non-return to service at Day 23 (81.7 vs. 64.2%), conception (78.8 vs. 61.5%), fertility (75.2 vs. 61.5%) and fecundity (0.77 vs. 0.62) were higher in ewes from SE than PG15 group (P < 0.05). However, no differences were observed in prolificacy (1.02 ± 0.16 vs. 1.01 ± 0,12) between groups (P > 0.05). Protein supplementation increased ovulation rate (1.30 ± 0.45 vs. 1.17 ± 0.40), prolificacy (1.18 ± 0.39 vs. 1.02 ± 0.16) and fecundity (0.94 vs. 0.77%; P < 0.05), but not non-return to service on Day 23 (83.8 vs. 81.7%), conception (82.9 vs. 78.8%) or fertility (79.1 vs. 75.2%; P > 0.05) in SE group. The supplement feed to PG15 ewes increased ovulation rate (1.35 ± 0.45 vs. 1.06 ± 0.25), prolificacy (1.25 ± 0.43 vs. 1.01 ± 0.12) and fecundity (0.79 vs. 0.62%; P < 0.05) to levels comparable to SE + FF ewes (P > 0.05). The magnitude of the increase in ovulation rate in PG15 was greater than in the SE group (27 vs. 11%; P < 0.05). However, non-return to service on Day 23 (65.1 vs. 64.2%), conception (63.3 vs 61.5%), and fertility rate (63.3 vs. 61.5%; P < 0.05) remained similar in PG15 supplemented or not supplemented ewes. In conclusion, a short-term protein supplementation before cervical time artificial insemination improved the reproductive performance of ewes synchronized with the PG15 protocol to levels comparable to the SE group.

Calm Merino ewes have a higher ovulation rate and more multiple pregnancies than nervous ewes.

In 1990, two selection lines of Merino sheep were established for low and high behavioural reactivity (calm and nervous temperament) at the University of Western Australia. Breeding records consistently showed that calm ewes weaned 10% to 19% more lambs than the nervous ewes. We hypothesise that calm ewes could have a higher ovulation rate than nervous ewes and/or calm ewes could have a lower rate of embryo mortality than nervous ewes. We tested these hypotheses by comparing the ovulation rate and the rate of embryo mortality between the calm and nervous lines before and after synchronisation and artificial insemination. Merino ewes from the temperament selection lines (calm, n=100; nervous, n=100) were synchronised (early breeding season) for artificial insemination (day 0) (intravaginal sponges containing fluogestone acetate and eCG immediately after sponge withdrawal). On day-17 and 11 ovarian cyclicity and corpora lutea, and on days 30 and 74 pregnancies and embryos/foetuses were determined by ultrasound. Progesterone, insulin and leptin concentrations were determined in blood plasma samples from days 5, 12 and 17. Ovarian cyclicity before and after oestrus synchronisation did not differ between the lines, but ovulation rate did (day-17: calm 1.63; nervous 1.26; P<0.01; day 11: calm 1.83; nervous 1.57; P<0.05). Ovulation rate on day 11 in nervous ewes was higher than on day-17. Loss of embryos by day 30 was high (calm: 71/150; nervous: 68/130); but nervous ewes had a lower proportion (15/47) of multiple pregnancies compared with calm ewes (30/46; P<0.01). Reproductive loss between days 30 and 74 represented 7.3% of the overall loss. Temperament did not affect concentrations of progesterone, but nervous ewes had higher insulin (32.0 pmol/l±1.17 SEM; P=0.013) and lower leptin (1.18 µg/l±0.04 SEM; P=0.002) concentrations than calm ewes (insulin: 27.8 pmol/l±1.17 SEM; leptin: 1.35 µg/l±0.04 SEM). The differences in reproductive outcomes between the calm and nervous ewes were mainly due to a higher ovulation rate in calm ewes. We suggest that reproduction in nervous ewes is compromised by factors leading up to ovulation and conception, or the uterine environment during early pregnancy, that reflect differences in energy utilisation.

Long term prostaglandin based-protocols improve the reproductive performance after timed artificial insemination in sheep.

The aim of the experiment was to evaluate the reproductive performance of ewes synchronized with two doses of prostaglandin F2α (PG) at different intervals and inseminated at a fixed time. During the breeding season (April to June), 370 multiparous Corriedale ewes were assigned to five groups according to body condition score and body weight, and synchronized with two doses of PG administered 7, 10, 12, 14 or 16 days apart (groups PG7, PG10, PG12, PG14 or PG16; n = 73, 76, 74, 72, 75; respectively). Cervical timed artificial insemination (Day 0) was performed at 48 ± 1.0 h (group PG7) or 56 ± 1.0 h (groups PG10, PG12, PG14 and PG16) after the second PG injection, with diluted fresh semen pooled from six adult rams. The percentage of ovulating ewes after the second PG injection and the ovulation rate (number of corpus luteum/ovulating ewes) were assessed on Day 10 by trans-rectal ultrasonography. The rate of non return to service (ewes not returning to service/inseminated ewes × 100; NRR-21) was evaluated using painted vasectomized rams. Pregnancy rate (pregnant ewes/inseminated ewes × 100) and prolificacy (foetuses/pregnant ewes) were determined on Day 60 by trans-abdominal ultrasonography. Higher NRR-21 and pregnancy rates was observed in groups PG12 (46.0%, 46.0%), PG14 (59.7%, 56.9%) and PG16 (58.7%, 56.0%) compared to PG7 (30.1%, 28.8%) and PG10 (30.3%, 30.3%; respectively P < 0.05). No significant differences were observed in the percentage of ovulating ewes, ovulation rate and prolificacy among groups (P > 0.05). Under the condition of this trial, 12, 14 or 16 days interval between PG injections enhances the pregnancy rate of ewes at cervical timed artificial insemination with fresh semen.

Concentrations of steroid hormones, estrous, ovarian and reproductive responses in sheep estrous synchronized with different prostaglandin-based protocols.

To determine estrous, ovarian and reproductive responses after different prostaglandin (PG)-based protocols, ewes were assigned to groups PG10, PG12, PG14 or PG16 (twoPG injections administered 10, 12, 14 or 16 days apart; respectively). Experiment I (n=132) was conducted to evaluate the estrous response, ovulation rate (OR), conception and fertility. Experiment II (n=24) was conducted to evaluate ovarian follicle growth, steroid concentrations and the interval from the second PG injection to estrus (PG-estrus) and ovulation (PG-ovulation). Estrous response was less with the PG16 (P<0.05) treatment, and the extent of estrous synchrony was greater with the PG10 and PG12 treatments. Ovarian follicle growth and the intervals for the variables PG-estrus, PG-ovulation and OR were similar among groups (P>0.05). From 8 to 4 days before estrus, progesterone (P4) concentrations were greater for the PG14 and PG16 than for the PG10 and PG12 (P<0.05) groups. There were more days where concentrations of P4 were above 3.18 nmol/L with the PG14 and PG16 than PG10 and PG12 (P<0.05) treatments. Use of the PG14 and PG16 treatments resulted in greater estradiol (E2) at estrus and 12h later than use of the PG10 and PG12 treatments. A positive correlation was observed between the duration of the luteal phase and maximum E2 concentrations, and between duration of the luteal phase and days with E2 concentrations above 10 pmol/L. Conception and fertility were greater with use of the PG14 compared with PG10 and PG12 (P<0.05) treatments. The administration of two PG injections 10, 12, 14 or 16 days apart resulted in different durations of the luteal phase that were positively associated with E2 concentrations and the reproductive outcome. The shorter luteal phases were associated with greater synchrony in time of estrus. The intervals for the variables PG-estrus, PG-ovulation and OR were similar among groups.

Protein supplementation during a short-interval prostaglandin-based protocol for timed AI in sheep.

The aim of this experiment was to improve the reproductive performance of a short-interval prostaglandin (PG)-based protocol for timed artificial insemination in sheep, using a short-term nutritional treatment. During the breeding season (March-April), 132 multiparous and 61 nulliparous Corriedale ewes grazing natural pastures (600 kg DM/ha, 8.5% CP), were allocated to two groups: 1, Control group (n=100) two injections of D-Cloprostenol (75 µg per dose, 7d apart: Synchrovine(®) protocol); and 2, Supplemented group (n=93) ewes in which stage of the oestrous cycle was synchronised with Synchrovine(®) protocol plus focus feeding of a protein supplement (33.8% CP) between PG doses (Day -7 to -2). Cervical AI was performed at fixed time (Day 0), 46 ± 1.0 h after the second PG injection using 150 million sperm per ewe. Ovulation rate (Day 10), pregnancy rate, prolificacy and fecundity at Day 69 were evaluated by ultrasonography. Ovulation rate at Day 10 (1.20 ± 0.05 vs. 1.22 ± 0.05), pregnancy (46 ± 0.05 vs. 56 ± 0.05), prolificacy (1.09 ± 0.04 vs. 1.06 ± 0.05), and fecundity (0.49 ± 0.06 vs. 0.59 ± 0.06) at Day 69, were similar between groups (P>0.05; Control and Supplemented group respectively). It is concluded that focus feeding for 6d with protein supplementation during a short-interval PG-based protocol (Synchrovine(®)) did not improve the reproductive outcome associated with this protocol.

Follicle development, endocrine profiles and ovulation rate in adult Merino ewes: effects of early nutrition (pre- and post-natal) and supplementation with lupin grain.

In adult ewes, we tested whether ovarian function, including the response to short-term supplementation, was affected by the nutrition of their mothers during the pre-/post-natal period. A 2×2 factorial design was used with nutrition in early life (low or high) and a 6-day supplement (with or without) as factors. All ewes received three prostaglandin (PG) injections 7 days apart, and the supplement (lupin grain) was fed for 6 days from 2 days after the second until the third PG injection. We measured reproductive and metabolic hormones, studied follicle dynamics (ultrasonography), and evaluated granulosa cell numbers, aromatase activity and oestradiol (E2) concentrations in follicular fluid in healthy follicles at days 3 and 7 of supplementation. Ovulation rate was increased by 25% by exposure to high pre-/post-natal nutrition (1.5 vs 1.2; P<0.05), in association with a small decrease in FSH concentrations (P=0.06) and a small increase in insulin concentrations (P=0.07). The number of healthy antral follicles was not affected. Acute supplementation increased the number of granulosa cells (3.7±0.2 vs 3.0±0.2 million; P<0.05) in the largest follicle, and the circulating concentrations of E2 (4.6±0.3 vs 3.9±0.3 pmol/l; P<0.05) and glucose (3.4±0.03 vs 3.3±0.03 mmol/l; P<0.01). Both early life nutrition and acute supplementation appear to affect ovulation rate through changes in glucose-insulin homoeostasis that alter follicular responsiveness to FSH and therefore E2-FSH balance.

Reproductive outcome with GnRH inclusion at 24 or 36h following a prostaglandin F2α-based protocol for timed AI in ewes.

The objective of this experiment was to study the reproductive performance obtained after a short-interval prostaglandin (PG) F2α-based protocol for timed artificial insemination (TAI) in sheep (Synchrovine®: two injections of PG 7 d apart), including a GnRH analogue at 24 or 36h after the second PG injection. The experiment involved 296 Corriedale ewes (206 multiparous and 90 nulliparous) grazing natural pastures during the breeding season (March-April; UTU "La Carolina", Flores Uruguay, 33° S-57° W). Ewes were assigned to three treatment groups: a) Synchrovine® (Control, n=101): two injections of D-Cloprostenol 75µg, 7 d apart, b) Synchrovine®+GnRH24 (n=98): Synchrovine® plus GnRH (busereline acetate 8.4µg) 24h after the second PG injection, and c) Synchrovine®+GnRH36 (n=97): Synchrovine® plus GnRH 36h after the second PG injection. All ewes were subjected to cervical TAI (Day 0), 44 to 47h after second PG injection, with fresh extended semen pool from six rams. Reproductive performance of ewes having ovulations and ovulation rate on Day 10, estrous cycle length in ewes that returned to estrus and non-return rate to estrus up to Day 22, fertility, prolificacy and fecundity on Day 70 were analyzed. Ewes having ovulations, ovulation rate, estrous cycle length and prolificacy did not differ between groups (P>0.05). However, non-return to estrus, fertility and fecundity was decreased in Synchrovine®+GnRH24 (P<0.05) and similar between Synchrovine® and Synchrovine®+GnRH36 (P>0.05). It was concluded that the reproductive performance obtained by Synchovine® TAI protocol was impaired by GnRH at 24h and not improved by GnRH administered at 36h after the second PG injection.

Embryo losses in sheep during short-term nutritional supplementation.

To test whether a nutritional supplement fed from 6 days before until 15 days after insemination reduces progesterone concentrations and increases embryo losses, Merino ewes were artificially inseminated (Day 0). Control ewes (n = 116) were not supplemented whereas Lupin6 ewes (n = 112) were supplemented with 500 g lupin grain daily for 6 days before insemination, and Lupin6+15 ewes (n = 122) from 6 days before until 15 days after insemination. There were no major differences between treatment groups in progesterone concentrations over the first 17 days of pregnancy. Embryo losses over Days 10-17 were lower in the Lupin6+15 than in the Control and Lupin6 groups, but the opposite occurred from Day 17-30. The concentrations of insulin and IGF-I were higher in Lupin6+15 ewes on Days 5, 12 and 17, compared with Lupin6 and Control ewes, while leptin concentrations decreased by Day 17 in the Lupin6+15 group. We conclude that feeding ewes for 15 days after mating improved embryo survival, which was associated with an increase in the concentrations of metabolic hormones and lower progesterone concentrations. However, the decrease in leptin concentrations promoted by the interruption of supplementation seems be linked to increased embryo mortality up to Day 30.

Effects of prostaglandin administration on ovarian follicular dynamics, conception, prolificacy, and fecundity in sheep.

Two experiments were conducted to determine the effects of prostaglandin administration on ovarian follicular dynamics, conception, prolificacy, and fecundity in sheep. During the breeding season, multiparous Corriedale ewes were randomly allocated to two groups: 1) PG group (n = 15 and n = 135 in Experiments I and II, respectively): synchronized with two injections of DL-Cloprostenol (125 µg) given 7 d apart, and inseminated at a fixed time (Day 0), 48 h after the second injection; and 2) Control group (n = 15 and n = 73 in Experiments I and II): ewes in spontaneous estrus inseminated at detected estrus. Ewes received 100 × 10(6) sperm by intrauterine AI. Ultrasonography was used to evaluate growth of the ovulatory follicle, ovulation rate (OR), conception rate, and prolificacy on Days 30 and 60. Ewes from the group PG had a larger (4.8 ± 0.5 mm, mean ± SEM; P < 0.05) ovulatory follicle that grew faster (1.2 ± 0.3 mm/d, P = 0.08), and a lower OR (1.37 ± 0.1, P < 0.05), compared to ewes from the Control group (3.9 ± 0.2 mm, 0.7 ± 0.2 mm/d, and 1.61 ± 0.1 respectively). Plasma progesterone concentrations from Days -6 to 1 were lower in the PG group (P < 0.05), but plasma estradiol concentrations were similar between groups (P > 0.05). Progesterone concentrations were similar between groups during the early luteal phase and on Days 12 and 17 (P > 0.05). The embryo recovery rate (Day 7) tended to be lower in the PG group (39 vs 64%, P = 0.08), but embryo quality did not differ between groups. Conception, prolificacy and fecundity, were lower in the PG than in the Control group (P < 0.05). Cumulative reproductive losses were similar between groups, but more twins were lost in the PG group (P < 0.05). We concluded that in ewes synchronized with PGF(2α) given twice, 7 d apart, lower reproductive performance was associated with an environment dominated by lower progesterone concentrations that stimulated the preovulatory follicle to grow faster and become larger; this was associated with lower rates of ovulation, conception, prolificacy, and fecundity.

Regulation of folliculogenesis and the determination of ovulation rate in ruminants.

The paper presents an update of our 1993 model of ovarian follicular development in ruminants, based on knowledge gained from the past 15 years of research. The model addresses the sequence of events from follicular formation in fetal life, through the successive waves of follicular growth and atresia, culminating with the emergence of ovulatory follicles during reproductive cycles. The original concept of five developmental classes of follicles, defined primarily by their responses to gonadotrophins, is retained: primordial, committed, gonadotrophin-responsive, gonadotrophin-dependent and ovulatory follicles. The updated model has more extensive integration of the morphological, molecular and cellular events during folliculogenesis with systemic events in the whole animal. It also incorporates knowledge on factors that influence oocyte quality and the critical roles of the oocyte in regulating follicular development and ovulation rate. The original hypothetical mechanisms determining ovulation rate are retained but with some refinements; the enhanced viability of gonadotrophin-dependent follicles and increases in the number of gonadotrophin-responsive follicles by increases in the throughput of follicles to this stage of growth. Finally, we reexamine how these two mechanisms, which are thought not to be mutually exclusive, appear to account for most of the known genetic and environmental effects on ovulation rate.

The use of a 'first-wave' model to study the effect of nutrition on ovarian follicular dynamics and ovulation rate in the sheep.

We have developed an experimental model in which groups of ewes are simultaneously experiencing the first ovarian follicular wave of their oestrous cycle. We used this 'first-wave model' in a 2 × 2 factorial experiment (ten ewes per group) to study the effect of body condition (BC) and a short-term supplement on follicular dynamics and ovulation rate. The 'first-wave' was established by giving ewes three injections of prostaglandin (PG), 7 days apart. The 6-day supplement (lupin grain) began 2 days after the second PG injection and continued until the third. Follicles were studied by ultrasound, and blood was sampled to measure glucose and hormones. The supplement increased (P<0.01) the concentrations of glucose, insulin and leptin, decreased FSH concentrations (P<0.01) and tended to increase oestradiol concentrations (P=0.06). The supplement tended to increase the number of 3 mm follicles (P=0.06). Compared with low-BC ewes, high-BC ewes had more follicular waves (P<0.05), higher concentrations of insulin, leptin and IGF1 (P<0.05) and tended to have higher FSH concentrations (P=0.09). Leptin and insulin concentrations remained high until the end of supplementation in high-BC ewes, whereas they decreased after the third day of supplementation in low-BC ewes. In conclusion, high concentrations of metabolic hormones in fat ewes are associated with the development of more follicular waves. When a supplement is superimposed on this situation, changes in glucose and metabolic hormones allow more follicles to be selected to ovulate.

Sexual experience and temperament affect the response of Merino ewes to the ram effect during the anoestrous season.

In seasonally anoestrous ewes of many breeds, the introduction of rams triggers an increase in gonadotrophin secretion that induces ovulation, a phenomenon known as the 'ram effect'. The ram effect is a practical method for mating ewes outside the natural breeding season, and also can provide synchronised lambing, but the variability of the response, especially in young animals, reduces its potential for widespread application. The aim of our study was to assess two factors that are thought to contribute to the variability in young ewes: temperament and sexual experience. We used anovulatory ewes from a flock that had been genetically selected for 'calm' or 'nervous' temperament and compared the endocrine and ovarian responses to the ram effect in four groups (each n=15): 'calm' and parous (3-6 years old); 'calm' and nulliparous (2 years old); 'nervous' and parous; and 'nervous' and nulliparous. Parous ewes, independently of their temperament, exhibited a faster endocrine response and a higher proportion of females cycling after ram introduction than nulliparous ewes. 'Nervous' ewes exhibited a higher proportion of females cycling after ram introduction than calm ewes, but only in the nulliparous group. We conclude that temperament exerts little influence on the response to the ram effect in sexually experienced ewes, and that females of 'nervous' temperament appear to respond better when sexually 'naive'. Both sexual experience and temperament need to be taken into consideration when flock management involves the ram effect. Finally, some ewes were cyclic at ram introduction, yet exhibited an increase in LH secretion even in the presence of high concentrations of progesterone. The mechanism by which the inhibitory effect of progesterone on LH secretion was bypassed needs to be clarified.

Effect of prepartum diet on postpartum ovarian activity in Holstein cows in a pasture-based dairy system.

The hypothesis was that supplementation during the late prepartum period will differentially affect reproductive and productive variables according to parity. Primiparous (n=22) and multiparous (n=22) pregnant autumn calving Holstein cows were stratified in two groups according to parity (primiparous or multiparous) and within each group were randomly assigned to two treatments: (a) low supplemented (LS) or (b) high supplemented (HS) prepartum diet. The LS group was offered 5.2 kg/cow/day (DM basis) of wheat silage, and the HS group 4.7 kg cow/day (DM basis)/of corn silage and 3.6 kg (DM basis) of wheat bran+12 g of urea. Both groups grazed on natural pastures. After calving, all cows received the same diet. The experimental period was from 3 weeks before calving to 7 weeks postpartum (PP); body condition score (BCS) and blood samples for hormonal analyses were obtained weekly and ovarian ultrasonography was conducted three times per week. The loss in BCS around calving was less pronounced in HS cows, but only multiparous supplemented cows maintained BCS throughout the study. Non-esterified fatty acids (NEFA) increased during the prepartum period in the LS but not in the HS cows, with peak values occurring on day 14 PP in all groups. During the remainder of the experiment NEFA was greater in LS than in HS cows. Prepartum treatment did not affect the proportion of cows that had ovulations from the first dominant follicle postpartum, but decreased the interval to first ovulation in multiparous cows (22.9 compared with 38.2 days; P<0.05). This was associated with greater plasma IGF-I concentrations at the time the dominant follicle of the first follicular wave reached its maximum diameter (8.0 compared with 3.6 nmol/L; P<0.05). However, prepartum treatment had no effect on onset of ovarian activity in primiparous cows. Supplementation had no effect on milk production or milk protein percentage but increased milk fat percentage. We conclude that feeding a high-supplemented prepartum diet to multiparous cows allowed them to maintain BCS around calving, and this was associated with greater concentrations of IGF-I and an earlier onset of estrous cycles after calving.