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Voluntary food intake, milk yield and composition, and blood metabolites were measured during the first 2 mo of lactation in draft broodmares fed diets containing either 95% hay and 5% concentrates (Diet F) or 50% hay and 50% concentrates (Diet C). Voluntary food intake was higher for mares fed Diet C than for those fed Diet F (22.9 vs. 21.4 kg dry matter in wk 4). Both diets, especially Diet C, were eaten in amounts exceeding the energy requirements. Daily milk yield in wk 4 was 26.4 kg and 23.4 kg for mares fed Diets C and F, respectively. Milk fat and protein concentrations were higher (P less than 0.01) for mares fed Diet F than for those fed Diet C and decreased (P less than 0.01) from colostrum (48 +/- 12 h after foaling to wk 8); lactose concentration was higher (P less than 0.05) for mares fed Diet C than for those fed Diet F and increased (P less than 0.01) from colostrum to wk 8. Minerals varied mainly with lactation stage. Milk fat was higher in linolenic acid and lower in linoleic acid for mares fed Diet F than for those fed Diet C. Glucose concentration was higher in plasma of mares fed Diet C; 3-hydroxybutyrate and acetate concentrations were higher in plasma of mares fed Diet F.

Preweaning piglet mortality is largely attributed to the incidence of low birth weight and birth weight variation within the litter. Therefore, developing strategies to increase within-litter uniformity of piglet birth weight is important. This study investigated the effects of different feeding strategies based on specific nutrient supplies in sow diet on the within-litter variation of piglet birth weight (BW0). Four batches of highly prolific crossbred Landrace × Large White sows were used. Three dietary treatments were compared: supplies of dextrose during the week before insemination (190 g/d) and of L-arginine (25.5 g/d) from d 77 of pregnancy until term (DEXA, n = 26); a dietary supplementation of L-arginine only (25.5 g/d), from d 77 of pregnancy until term (ARGI, n = 24); and no supplementation to a standard gestation diet (CTL; n = 23). Total born piglets (TB), i.e., piglets born alive (BA) and stillborn piglets, were numbered and weighed at birth and at weaning. Data were analyzed by ANOVA using the MIXED procedure in a model that included dietary treatment (ARGI, DEXA, and CTL), initial parity (1, 2 and 3, 4, and more), and backfat thickness (below or above the average value at the onset of the experiment: 15.7 mm) as the main effects and batch as random effect. The treatment did not influence (P > 0.10) the number of piglets at birth (on average 15.6 ± 3.8 and 14.2 ± 3.6 for TB and BA, respectively) or piglet BW0 (on average 1.48 ± 0.26 and 1.50 ± 0.26 kg for TB and BA, respectively). The coefficient of variation of piglet BW0 (CV(BW0)) was less in litters from ARGI sows than in litters from CTL sows and intermediate in litters from DEXA sows (for TB: 21.4, 23.4, and 25.7%, P = 0.08; for BA: 20.6, 22.5, and 25.4%, P = 0.03, in the ARGI, DEXA, and CTL groups, respectively). Irrespective of diet, CV(BW0) was less (P < 0.01) in litters with 16 TB piglets or less than in the largest litters (20.9 vs. 26.5%). Litter growth rate during lactation and litter size at weaning were not influenced (P > 0.10) by dietary treatments. In conclusion, supplementing gestation diet with L-arginine during the last third of pregnancy reduced within-litter variation of piglet birth weight. Combining L-arginine dietary supply with a supplementation of dextrose before insemination provided no additional benefit.

The yields and composition of milk from nursing mares were studied during the first two months of lactation in 11 mares of heavy breeds (784 kg). Daily yield increased from 21-7 to 24-6 kg between weeks 1 and 8 of lactation. Fat, protein, gross energy and Ca concentrations significantly decreased when lactose content increased during this period. Individual variations were higher for yield than for composition. Casein, whey protein and non-protein N (56, 34 and 10% of crude protein, respectively) and amino acid composition did not vary between weeks 1 and 8 of lactation.Information on the composition of milk from nursing mares is extensive: some 20 authors have studied the effects of lactation stage on milk fat and/or crude protein (Doreau & Boulot, 1989a). However, some components, such as those containing N, have seldom been studied in relation to lactation stage. Because of problems associated with the determination of milk production by lactating mares, simultaneous determinations of milk yield and composition are few. Moreover, some results are questionable because inaccurate methods were used (Doreau & Boulot, 19896). The most reliable are probably those of Oftedal et al. (1983).This trial was performed on a large number of mares managed individually under the same feeding scheme, in order to provide information on both milk yield and composition, and on nutrient output, and their variations according to individuals and to lactation stage. Special emphasis was placed on N fractions and amino acid composition. MATERIAL AND METHODS Animals and dietsEleven multiparous mares of heavy French breeds (Bretonnes, Comtoises), aged 5 to 16 years and weighing after foaling 784 + 39 kg, were managed indoors in individual boxes for the last month of pregnancy and for the first 2 months of lactation. All mares were in good condition at foaling. They were fed on a constant composition diet based on 85% natural grassland hay, first cut, and 15% concentrates containing 50% barley, 45% soyabean meal, 3 % molasses and 2% mineral premix. This diet was offered ad lib., with a mean of 10% hay refusals. The hay-concentrate ratio was adjusted daily. Hay was delivered 3 times/d and

SummaryThe yield and composition of milk from nursing mares were studied during the first 2 months of lactation in two groups of six and five saddle mares respectively made thin or fat before foaling, then fed ad lib. post partum. Milk yield did not significantly vary with body condition (16·5 and 15·4 kg/d for fat and thin mares respectively). Milk from fat mares had a higher fat content than milk from thin mares; the reverse was found for protein. The composition of milk fat was modified: milk of fat mares was poorer in short- and medium-chain fatty acids (C8-C14). Milk fat output was affected by body condition: 252 and 187 g/d for fat and thin mares respectively. This can be explained by a difference in lipid mobilization, as shown by variations in non-esterified fatty acids.

Data from in vivo digestibility trial with four to six horses fed twenty‐seven forage‐based diets are used to calculate prediction equations for the digestibility of dry and organic matter, based on the crude ash (CA), crude protein (CP) and crude fibre (CF) contents of diets and faeces. The most precise prediction of dry‐matter digestibility (r.s.d. = 0.032, R2= 0.80) was derived from a multiple regression including faecal (CP, CF) and dietary parameters (CF). Among faecal parameters, CP was the best single predictor of both digestibility (r.s.d) = 0.040, r2= 0.63) and dietary CP content (r.s.d = 0.028, r2= 0.59). For biological reasons we propose a non‐linear model that allows prediction of dry‐ and organic‐matter digestibility from faecal CP Content with reasonable Precision (r.s.d = 0.038, 0.036, r2= 0.65, 0.74, respectively). This will be adequate for many studies, especially for free‐living animals in rangelands.

Introduction.

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