EFFECT OF NUTRITIONAL FLUSHING, SUPPLEMENTAL FAT AND SUPPLEMENTAL LYSINE FROM PUBERTY TO BREEDING AND DURING EARLY GESTATION ON REPRODUCTIVE PERFORMANCE OF GILTS

1988 ◽  
Vol 68 (3) ◽  
pp. 941-951 ◽  
Author(s):  
R. R. GRANDHI
Keyword(s):  
Survival Rate ◽  
Reproductive Performance ◽  
Control Diet ◽  
Allantoic Fluid ◽  
Progesterone Level ◽  
Embryo Survival ◽  
Early Gestation ◽  
Treatment Groups ◽  
Animal Fat ◽  
Supplemental Fat

Four experiments were conducted, using a total of 356 Landrace × Yorkshire crossbred gilts, to determine the influence of flushing, supplemental fat and supplemental lysine fed from puberty to breeding (exps. 1 and 2) and from puberty through early gestation (exps. 3 and 4) on the reproductive performance of gilts. All gilts were housed in total confinement and fed ad libitum a 16% protein swine grower diet until 150 d of age. The diet was then restricted to 2 kg d−1 until puberty. The treatment diets fed from puberty to breeding in exps. 1 and 2 were: (1) control, a 12% protein barley-soybean meal gestation diet fed at 2 kg d−1 (24.4 MJ DE d−1); (2) flushing, control diet fed at 3 kg d−1 (36.6 MJ DE d−1; (3) animal fat, control diet fed at 2 kg d−1 plus 622 g of fat premix (36.6 MJ DE d−1; and (4) lysine, control diet with supplemental lysine (14 g d−1) fed at 2 kg d−1 (24.4 MJ DE d−1). After breeding, all gilts were fed control diet at 2 kg d−1 until approximately 30 d at gestation. In exps. 3 and 4, the same treatment diets were used except flushing was omitted and they were fed from puberty to approximately 30 d of gestation. No significant differences (P > 0.05) among the treatment groups were found in any of the experiments for the number of corpora lutea and normal embryos, and ovarian, uterine, and fetal weights. In exp. 2, the embryo survival rate (%) was significantly lower (P < 0.05) in the flushing (81.7 ± 3.3) and animal fat (78.3 ± 3.3) groups than in the control (92.9 ± 3.0); however, the lysine (88.8 ± 3.5) group did not differ significantly from the other groups. The embryo survival rate was also reduced (P < 0.05) by supplemental fat (81.5 ± 2.7) when compared to the control (86.8 ± 3.0) and lysine (88.8 ± 2.7) diets in exp. 3 but not in exp. 4. The serum progesterone level (ng/mL−1) was lower (P < 0.05) in the animal fat group (4.1 ± 0.6) than in the control (6.3 ± 0.6) and lysine (6.1 ± 0.6) groups in exp. 4. However, progesterone level of allantoic fluid in exp. 4 and estrone sulfate levels of both serum and allantoic fluid in exps. 3 and 4 were similar for the three treatment groups. The overall results indicated that flushing, supplemental fat or supplemental lysine fed from puberty to breeding, and supplemental fat or supplemental lysine fed from puberty through early gestation did not improve the ovulation rate, embryo survival or fetal development in gilts. Key words: Ovulation rate, embryo survival, flushing, fat, lysine, hormones, gilts

Effect of feeding supplemental fat or lysine during the postweaning period on the reproductive performance of sows with low or high lactation body weight and fat losses

1992 ◽  
Vol 72 (3) ◽  
pp. 679-690 ◽  
Author(s):  
R. R. Grandhi
Keyword(s):  
Weight Loss ◽  
Reproductive Performance ◽  
High Weight ◽  
Control Diet ◽  
Ovulation Rate ◽  
Lactation Period ◽  
Embryo Survival ◽  
Fetal Survival ◽  
Supplemental Fat ◽  
High Lactation

The effects of feeding supplemental fat or lysine during the postweaning period on breeding and subsequent reproductive performance were determined in two experiments of a 2 × 3 factorial design, using 168 Landrace × Yorkshire first-parity (exp. 1) and 180 Yorkshire second-parity (exp. 2) sows. At the end of lactation, they were divided into two groups: LWL (< 14 kg) and HWL (> 14 kg) based on 3 wk lactation weight loss. The three experimental diets fed during the postweaning period were: (1) control; a 12% gestation diet fed 2 kg d−1 (24.7 MJ DE, 9.4 g lysine d−1); (2) Fat; control diet plus animal fat to provide approximately 50% more daily energy intake (37.0 MJ DE d−1); and (3) Lysine; control diet plus lysine to provide approximately 50% more daily lysine intake (14.4 g d−1). After breeding, all sows were fed the control diet at 2 kg d−1, and they were killed at 30 d of gestation to evaluate their reproductive performance. High weight loss during the lactation period increased the incidence of anestrus and reduced the pregnancy rate in first-parity sows. Feeding supplemental fat was beneficial in increasing the proportion of sows in estrus within 7 d postweaning and the pregnancy rates of first-parity sows with high lactation weight loss. Supplemental fat also had a beneficial effect on ovulation rate, the number of normal embryos, fetal survival and the fetal weights, whereas supplemental lysine improved only fetal weights. Feeding supplemental fat or lysine improved only ovulation rate in second-parity sows with high lactation weight loss. The results indicated that feeding supplemental fat or lysine can improve the postweaning reproductive performance of sows that had high weight and fat losses during lactation. Key words: Sows, estrus, ovulation, embryo survival, fat, lysine

THE INFLUENCE OF FEEDING LEVEL DURING LACTATION ON THE OCCURRENCE AND ENDOCRINOLOGY OF THE POSTWEANING ESTRUS IN SOWS

1987 ◽  
Vol 67 (2) ◽  
pp. 405-415 ◽  
Author(s):  
R. N. KIRKWOOD ◽  
S. K. BAIDOO ◽  
F. X. AHERNE ◽  
A. P. SATHER
Keyword(s):  
Reproductive Performance ◽  
Feed Intake ◽  
Crude Protein ◽  
Gonadotropin Releasing Hormone ◽  
Embryo Survival ◽  
Treatment Groups ◽  
Feeding Level ◽  
Low Level ◽  
Sow Lactation ◽  
Estradiol 17Β

Two experiments were performed with 78 second parity Lacombe sows to determine the influence of nutrition on reproductive performance. During a lactation of 35 d sows were fed daily either 3 (L) or 6 kg (H) of a diet having 16% crude protein and 12.5 MJ DE kg−1. For exp. 1, six L- and six H-fed sows were given an intravenous injection of gonadotropin releasing hormone (GnRH) at 21 d of lactation and blood was sampled at −30, −10, 0, 10, 20, 30, 45, 90 and 120 min from the time of injection. Prestimulation luteinizing hormone (LH) levels were lower for L-fed than for the H-fed sows (1.34 ± 0.1 vs. 1.93 ± 0.2 ng mL−1' P < 0.02). Peak LH levels achieved after UnKH injection, however, did not differ significantly (5.0 ± 0.6 and 5.8 ± 0.5 ng mL−1 for L and H sows, respectively). In exp. 2, 38 sows were fed the H and 40 fed the L level of feed throughout a 5-wk lactation. As expected, low-level feeding in lactation resulted in a greater body weight and backfat loss (17.4 ± 1.6 vs 41.2 ± 2.3 kg and 3.2 ± 0.4 vs. 6.3 ± 0.1 mm; P < 0.001 for both). Low-level feeding also resulted in an increased incidence of anestrus (15.0 vs. 0.0%) and an extended remating interval (140.7 ± 11.7 vs. 103.4 ± 2.1 h; P < 0.05). At the postweaning estrus, sows were inseminated with either fresh (F) or thawed (T) semen. Treatment groups were thus HF, LF and LT. Pregnancy rate was influenced by both feed level and semen type (90, 72, 69 and 39% for groups HF, HT, LF and LT, respectively). Ovulation rate was unaffected by feed intake (18.7 ± 0.9 vs. 18.2 ± 0.5 for L and H sows, respectively) but embryo survival was influenced by both feed intake and semen type (82.7 ± 2.5, 46.4 ± 9.7, 68.3 ± 9.6 and 53.7 ± 9.8% for groups HF, HT, LF and LT respectively). Eight H and twelve L-fed sows were blood-sampled via indwelling vena caval cannulae at 6-h intervals from weaning until the end of estrus. No treatment effect was noted for plasma levels of LH, growth hormone, estradiol-17β or testosterone during this period. It was concluded that low-plane feeding in lactation and the consequent increased weight and backfat loss reduce reproductive performance of sows. However, the mechanism(s) controlling this effect remain to be fully elucidated. Key words: Sow, lactation, nutrition, estrus

Apparent absorption and retention of nutrients during the postweaning period in sows fed supplemental fat or lysine

1994 ◽  
Vol 74 (1) ◽  
pp. 123-128 ◽  
Author(s):  
R. R. Grandhi
Keyword(s):  
Weight Loss ◽  
Control Diet ◽  
Canola Meal ◽  
Fat Absorption ◽  
Nitrogen Absorption ◽  
Apparent Absorption ◽  
Animal Fat ◽  
Energy Retention ◽  
Supplemental Fat ◽  
Effect Of Feeding

A total of 36 first-parity Landrace × Yorkshire sows and 17 second-parity Yorkshire sows were used in separate metabolism trials of a 2 × 3 factorial design with two lactation (21–d) weight-loss groups and three postweaning treatment diets to determine the effect of feeding supplemental fat or lysine on apparent absorption and retention of nutrients during the postweaning period. Following a 5-wk lactation, sows were housed in individual sow metabolism stalls equipped for separate collection of feces and urine. The three treatment diets fed during the postweaning period were (1) control — a barley – canola meal gestation diet (12.4 MJ DE, 4.7 g lysine kg−1, and 12% protein) fed 2 kg d−1, (2) fat — the control diet plus animal fat premix to provide approximately 50% more DE d−1, and (3) lysine — the control diet with supplemental lysine to provide approximately 50% more lysine d−1. Feeding supplemental fat increased (P < 0.05) fat absorption and energy retention in sows of both parities. Water intake and absorption were reduced by feeding supplemental fat in first-parity sows. Feeding supplemental lysine increased nitrogen absorption in first-parity sows. The absorption and retention of both Ca and P were also higher in first-parity sows fed supplemental fat or lysine. The results indicated that feeding supplemental fat or lysine during the postweaning period may improve the absorption and retention of certain nutrients in sows. Key words: Postweaning, sows, nutrients, absorption, retention

Partial replacement of fishmeal with soybean meal and distillers dried grain solubles (DDGS) as alternative protein sources for milkfish, Chanos chanos (Forsskal, 1775) fingerlings

2020 ◽  
Vol 67 (4) ◽  
Author(s):  
S. Bharathi ◽  
Cheryl Antony ◽  
C. B. T. Rajagopalsamy ◽  
A. Uma ◽  
B. Ahilan ◽  
...  
Keyword(s):  
Survival Rate ◽  
Soybean Meal ◽  
Body Weight Gain ◽  
Control Diet ◽  
Partial Replacement ◽  
Chanos Chanos ◽  
Treatment Groups ◽  
Protein Sources ◽  
Alternative Protein ◽  
Significant Difference

A 60 days feeding trial was conducted to investigate partial replacement of fishmeal (FM) with either soybean meal (SBM) or distillers dried grain solubles (DDGS) as alternative protein sources for milkfish, Chanos chanos fingerlings. Nine experimental diets were formulated with either fishmeal or with two alternative protein sources such as SBM or DDGS at three protein levels (35, 40 and 45%). Milkfish fingerlings (270 nos.) with mean length and weight of 5.24±0.03 cm, 1.25±0.05 g were selected for the study and in total there were 9 treatments in triplicates. The experimental diets were: F35 (35% CP - FM diet), F40 (40% CP - FM), F45 (45% CP - FM), FS35 (35% CP - FM + SBM), FS40 (40% CP - FM + SBM), FS45 (45% CP - FM + SBM), FD35 (35% CP - FM + DDGS), FD40 (40% CP - FM + DDGS), FD45 (45% CP - FM + DDGS). Diets incorporated with fishmeal alone served as control diet for this experiment. We observed that, final weight was significantly (p<0.05) higher for fishmeal based diet irrespective of the crude protein level. The same trend was observed for body weight gain for FM based diet. Specific growth rate (SGR) was found to be more than 2% per day for all the experimental diets fed fish and FD45 showed the lowest SGR compared to other treatment groups. Similarly FD45 had poor feed conversion ratio (FCR) when compared to other dietary groups. Survival rate of the fingerlings was found to be significantly higher for all FM diets (80%), FS35 (80%) and FD35 (80%) diet fed groups, whereas FD45 dietary group showed significantly lower survival rate (60%). Higher amylase activity was observed in F40 diet, higher lipase enzyme activity in FS 35 diet, while higher protease activity was recorded in F35 diet and the values showed significant difference (p<0.05) between different treatment groups. Results of the study, clearly indicate that soybean meal (FS35) could be used to partially replace the fishmeal in the diet of milkfish fingerlings.

Studies in sow reproduction 5. The effect of lactation length of the sow on the subsequent embryonic development

1976 ◽  
Vol 22 (1) ◽  
pp. 79-85 ◽  
Author(s):  
M. A. Varley ◽  
D. J. A. Cole
Keyword(s):  
Survival Rate ◽  
The Other ◽  
Plasma Samples ◽  
Progesterone Concentration ◽  
Embryo Survival ◽  
Plasma Progesterone ◽  
Treatment Groups ◽  
Lactation Length ◽  
Sow Reproduction ◽  
Sampling Times

SummaryForty-five female pigs (sows) were allocated at random to one of three lactation lengths: 7 days, 21 days, 42 days. All sows were remated at the first post-weaning oestrus and were slaughtered at 20 days post coitum. The reproductive tracts were removed, dissected and examined. Ovulation rates as determined by luteal count were similar for all three groups, but the number of viable embryos decreased significantly (P < 0·05) from 13·0 for the 42-day lactation group to 9·2 for the 7-day lactation group. This difference was reflected in a significant (P < 0·01) reduction in the percentage embryo survival rate as lactation length was reduced. Uterine lengths for the 7-day lactation group were significantly (P < 0·05) shorter than the other two groups. Six sows in each treatment group were blood sampled: at weaning, at remating, at 2 days post-mating, at 10 days post-mating and at 20 days post-mating. The plasma samples obtained were assayed for progesterone. No differences were observed between treatment groups for plasma progesterone concentration at any of the sampling times. It is concluded that the reduction of the litter size at the next farrowing following a short lactation length is largely a result of increased embryo death in the first 20 days of gestation.

The effect of changes in feed intake around the time of insemination on systemic progesterone and embryo development and survival in cattle.

2001 ◽  
Vol 26 (2) ◽  
pp. 381-384
Author(s):  
L.D. Dunne ◽  
M.G. Diskin ◽  
M.P. Boland ◽  
K.J. O'Farrell ◽  
J.M. Sreenan
Keyword(s):  
Survival Rate ◽  
Embryo Development ◽  
Feed Intake ◽  
Cell Number ◽  
Early Embryo ◽  
Total Protein Content ◽  
Embryo Survival ◽  
Treatment Groups ◽  
Embryo Recovery ◽  
Significant Difference

AbstractEarly embryo loss is the major cause of reproductive failure in cattle. The objective of this study was to investigate the effect of changes in feed intake around the time of insemination on systemic progesterone and on embryo development and survival and in cattle. Nutrition treatments were designed to provide 0.8 times (Low, L) or twice (High, H) maintenance energy requirements. Oestrus was synchronised in heifers (n=314) using two injections of prostaglandin (PG; 50 μg Cloprostenol, Estrumate) administered 10 days apart. On the day of oestrus following the first PG injection, heifers were randomly allocated to L or H (pre-AI). At the oestrus following the second PG injection, heifers were inseminated with semen from the same Limousin bull and on the following day were randomly allocated to either L or H until embryo recovery at day 8 (n=25), 14 (n=57) or 16 (n=71) or pregnancy diagnosis at day 30 (n=161). Hence there were four nutrition treatments; L-L, L-H, H-H and H-L. There was no significant difference in embryo survival rate determined at day 14, 16 or 30 and so the data were combined for analysis. Overall embryo survival rate was significantly lower (P<0.001) in H-L (0.37) than L-L (0.70), L-H (0.71; P<0.001) or H-H (0.68; P<0.01) treatment groups. Nutrition treatment did not affect systemic progesterone measured on days 4, 5, 6 or 7 of the pre- or post-AI oestrous cycle. The total cell number of 8-day-old blastocysts was not significantly affected by nutrition treatment neither was the length, diameter or estimated total protein content of 14-day-old embryos. Reducing energy intake immediately after AI reduced embryo survival rate but there was no evidence that this effect was mediated through changes in systemic progesterone.

Embryo survival, but not first-parity litter size, is increased when gilts are fed diets supplemented with omega-3 fatty acids from fish oil

2013 ◽  
Vol 53 (1) ◽  
pp. 57 ◽  
Author(s):  
R. J. Smits ◽  
B. G. Luxford ◽  
M. Mitchell ◽  
M. B. Nottle
Keyword(s):  
Fish Oil ◽  
Litter Size ◽  
Reproductive Performance ◽  
Partial Replacement ◽  
Omega 3 ◽  
Large White ◽  
Embryo Survival ◽  
Early Gestation ◽  
Ad Libitum ◽  
Farrowing Rate

The response in reproductive performance when pigs are fed diets supplemented with fats high in polyunsaturated fatty acids (PUFA) has not been widely studied. Improved fertility has been reported in sows and other species fed diets with added fish oil, a rich source of omega-3 PUFA, but results are inconsistent. The aim of the present study was to determine the effect of the duration and the level of supplementation of omega-3 PUFA from fish oil on the reproductive performance of gilts. In Experiment 1, 570 Large White and Landrace purebred gilts were fed ad libitum either an unsupplemented diet containing tallow (Control) or a diet containing 3 g fish oil/kg (Omega-3) as a partial replacement for tallow from 24 weeks (Omega-3 for 6 weeks) or 27 weeks of age (Omega-3 for 3 weeks) before mating. Liveweight and backfat gain between 24 weeks of age and mating were recorded. Gilts were then fed an unsupplemented diet during gestation and farrowing rate and first litter size were recorded. In Experiment 2, 356 Large White × Landrace F1 cross gilts were fed ad libitum diets containing either 0, 3 or 10 g fish oil/kg of diet as a partial replacement of tallow from 24 weeks of age and continued after mating at 2.2 kg/day until slaughter at 25 days of gestation. Pregnancy rate, ovulation and embryo survival were recorded. Data were analysed by general linear model ANOVA and Chi-square methods. In Experiment 1, there was no increase in farrowing rate or litter size born in gilts fed the omega-3-supplemented diet for either 3 or 6 weeks before mating compared with Control gilts. In Experiment 2, supplementation with omega-3 PUFA from 24 weeks of age through to mating and continued during early gestation did not increase ovulation rate but there was a trend (P < 0.10) for an increase in embryo survival measured at Day 25 of gestation in gilts fed diets containing fish oil. Embryo survival was higher in gilts fed diets containing 3 g fish oil/kg of diet than in those fed the Control diet (P < 0.05). Increasing the supplementation level to 10 g fish oil/kg did not increase embryo survival further. In both experiments, supplementation of omega-3 as fish oil did not affect the onset of oestrous, gilt removal and weight and backfat gain. In conclusion, supplementation of omega-3 PUFA before mating did not improve farrowing rate or litter size in gilts. It may be necessary to continue feeding diets with low concentrations of fish oil during early gestation to maximise the reproductive response to elevated omega-3 PUFA.

scholarly journals The effect of energy intake on development and reproduction of gilts.

1984 ◽  
Vol 32 (4) ◽  
pp. 328-329
Author(s):  
L.A. den Hartog
Keyword(s):  
Birth Weight ◽  
Survival Rate ◽  
Standard Deviation ◽  
Energy Intake ◽  
Reproductive Performance ◽  
Metabolizable Energy ◽  
Embryo Survival

680 Dutch Landrace gilts were fed diets containing 3.0, 2.5, 2.1 or 1.8 times the metabolizable energy required for maintenance for 26 wk beginning at 12 wk of age. Gilts not showing oestrus by 38 wk of age were hormonally induced. The number of gilts showing spontaneous oestrus, embryo survival rate, number of liveborn piglets per litter, av. piglet birth weight and homogeneity of the litter (standard deviation of birth weight within a litter) were not affected by energy intake. The number of liveborn piglets per 100 gilts in the litters conceived to insemination at the 1st spontaneous oestrus was 386, 399, 437 and 438 for the 4 diets resp.; when data for hormonally induced gilts were included, the corresponding values were 485, 486, 599 and 579, indicating that in terms of reproductive performance, when the diet contains adequate protein, there is no need to supply more than 2.1 times the metabolizable energy required for maintenance. (Abstract retrieved from CAB Abstracts by CABI’s permission)

scholarly journals 88 Benefits of increasing amino acid intake in late gestation in prolific sows

2020 ◽  
Vol 98 (Supplement_3) ◽  
pp. 76-76
Author(s):  
Ron Ball ◽  
Crystal L Levesque ◽  
D J Cadogan
Keyword(s):  
Birth Weight ◽  
Amino Acid ◽  
Reproductive Performance ◽  
Essential Amino Acid ◽  
Control Diet ◽  
Genetic Selection ◽  
Late Gestation ◽  
Negative Effects ◽  
Amino Acid Levels ◽  
The Many

Abstract Most sows are fed a constant energy and amino acid supply throughout gestation, in line with the recommendations of most authorities and swine genetic companies. These recommendations for sow feeding have seen little change in decades, despite the many ways that sows have changed dramatically in reproductive performance. Beginning in about the year 2000, sow litter size has steadily increased as a result of genetic selection. With this increase in litter number has been a steady decline in birth weight, and the resulting negative effects of lower birthweight on subsequent piglet performance. Many experiments using so-called ‘bump’ feeding, or increased energy intake in late gestation, have been conducted in attempts to arrest this decline in birthweight and piglet performance. Generally, these experiments have shown little to no improvement in birthweight and often have negative effects on sow feed intake during gestation. These experiments have ignored the fact that the energy:amino acid ratios (lysine, threonine, isoleucine, tryptophan) in late gestation are different than during early and mid-gestation. In recent research in Australia we hypothesised that rapidly increasing essential amino acid levels in late gestation would increase birth weight and potentially improve subsequent reproductive performance. Three hundred and thirty-four multiparous PIC sows (average parity 3.6, average LW 261 kg) were housed in a dynamic gestation pen after mating and randomly assigned to one of two diet regimes. Two 13.5 MJ/kg DE gestation diets were formulated and created by blending in an ESF. The Control diet contained 0.48 g SID lysine per MJ DE and SID threonine, methionine+ cysteine, isoleucine and tryptophan at 68%, 65%, 58% and18% of SID lysine and offered at 2.2kg/day from d 28 to d 110. Sow were then moved to the farrowing house and placed on a lactation diet at 3.5kg/d. The Treatment diet contained 0.55 g SID lysine/MJ DE and SID threonine, methionine+cysteine, isoleucine and tryptophan at 78%, 65%, 60% and 20% of SID lysine and offered at 2.1kg/d from d 28 to d 85 and then increased to 2.4 kg/d to d 110 d. Increasing essential amino acid levels in late gestation increased gestational weight gain (5.6 kg, P=0.004), increased total litter birth weight (1.25 kg, P=0.003), and increased the birthweight of liveborn pigs from 1.286 to 1.329 kg, (P=0.04). There was no significant effect on the total number born or born alive. Piglet performance is not available because this commercial farm practices cross-fostering. Effects of continuation of this feeding regime in the same sows during subsequent parities is currently being evaluated.

Reproductive performance of group-synchronized Merino d'Arles and Romanov crossbred ewes. 1. A note on the effects of lactation on fecundity

1977 ◽  
Vol 24 (1) ◽  
pp. 113-116 ◽  
Author(s):  
F. J. Galindez ◽  
M. Prud'hon ◽  
G. Reboul
Keyword(s):  
Treatment Group ◽  
Reproductive Performance ◽  
The Other ◽  
Fertility Level ◽  
Homogeneous Groups ◽  
Treatment Groups ◽  
Significant Superiority

SUMMARYFifty-six Merino d'Aries and 56 Romanov × Merino crossbred lactating ewes were divided into two treatment groups, one (T1) with a ewe-to-ram ratio of 48: 1 (24 Merino and 24 crossbred) and the other (T2) of 64: 1 (32 Merino and 32 crossbred).Intravaginal sponges with 40 mg FGA (Searle) were inserted in two subgroups at 8-day intervals and withdrawn after 12 and 16 days in situ, in four equal groups at 4-day intervals. A dose of 400 IU pregnant mare's serum gonadotrophin (PMSG) was applied at sponge withdrawal.Fertility after two oestrous cycles was equally satisfactory in both treatments, though it was lower in treatment group T2. This could be due to the significantly low (P<0·01) number of Merino ewes raddled by the T2 ram (0·33 Merino against 0·92 crossbred) suggesting preferential behaviour by the ram in this treatment.Comparisons between breeds show a slight superiority in the fertility of crossbred ewes and a highly significant superiority in prolificacy These results suggest that using the described method, 2% of rams seems more than adequate to mate with progestagen-synchronized ewes with a satisfactory fertility level. It is, however, recommended to use homogeneous groups of ewes.

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