Yield and composition of milk from lactating mares: effect of lactation stage and individual differences

Abstract

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

Mare milk nitrogen fractions during lactation and determination by reversed-phase HPLC of the major whey proteins

“…Non-protein N decrease of the milk from the early lactation phases (day 4 to day 60) was in substantial agreement with those observed by other authors (Doreau et al 1990;Martin et al 1992;Csapó-Kiss et al 1995). Other studies found no significant variations (Oftedal et al 1983;Oftedal and Jenness 1988) or an irregular trend.…”

“…The same trends were observed in other breeds and/or for shorter lactation periods (Neseni et al 1958;Bowman and van der Schee 1978;Gibbs et al 1982;Oftedal and Jenness 1988;Doreau et al 1990;Smolders et al 1990;Mariani et al 1993;Csapó-Kiss et al 1995). Concerning the casein N content variations, Storch (1985) reported an irregular non-significant trend, probably because in this case he considered bulk mare's milk, and the lactation stage was not clearly defined.…”

“…For most Authors (Minieri and Intrieri 1970;Doreau et al 1990), excluding colostrum and the short transition phase, the lactation stage does not have a significant effect on the casein proportion trend.…”

Protein, amino acid and energy requirements of weanling foals and yearlings

“…The average intake of 13.7 g/d presented in Table 2 was deemed, therefore, to be suitable for weanlings, and involved no detrimental effects. On the other hand, the methionine content of mare's milk is low (Pelfonen et al 1980;Doreau et al .1990), and methionine can not be suggested to be a limiting amino acid for growing horses. Data on other amino acids in foals are inadequate to establish any accurate recommendations.…”

“…Data on other amino acids in foals are inadequate to establish any accurate recommendations. However, data concerning the intakes and blood levels of these amino acids fl-ab, 2) may be indicative in this respect, The intakes of nine essential amino acids by weanlings (250 kg) at the end of nursing period can be calculated, assuming a milk production of 10 kg with a protein content 1 ,B-1 .9% (Grbbs et al,'1982;Burns et al 1992), and the amino acid contents reported by Peltonen et al, (1980) and Doreau et al (1990) at the end of lactation, as well as feed intake of foals as given by DLG (1984) andiVRC (1989), and using the amino acid contents given for typical solid feeds. E.9., the calculated lysine intake, approximately 35 g/d with 13,5 g of it obtained from the milk, corresponds to the range of recommended levels for weanling foals.…”