-An increase in milk somatic cell count is often observed in commercial herds when cows are on pasture during summer. The objective of this study was to check, in experimental conditions, if this effect is due to the turning out to pasture.

Résumé — Dans 3 essais qui se sont déroulés pendant les 6 premières semaines de la lactation, l'effet de la complémentation des rations de total) was studied in 3 trials carried out during the first 6 weeks of lactation. In each trial, cows were divided into 2 groups, one of which was supplemented with methionine supplied in decreasing quantities between each of the 3 successive periods of 2 weeks : 20 g, 12 g and 6 g in trials 1 and 2 respectively and, on an average, 18 g, 10 g and 5 g in trial 3 where the quantities offered were individually adjusted to the expected milk production. The basal diet comprised grass silage fed ad libitum and hay fed in limited amounts in trials 1 and 2 and maize silage in limited amounts in trial 3. In the 3 trials, concentrate was offered in limited quantities adjusted for each cow to its expected milk production. The supply of protected D,L methionine on average did not modify milk production, milk composition, feed intake (trials 1 and 2) or liveweight variations during the 6 experimental weeks.

The plant-related factors of variation were first examined : the level of grass intake was, on an average, very similar between the first and the second growth cycle. During the first cycle it decreased from one week to another; the effect of dry matter content was not significant during our observations and that of digestibility was only significant for amounts ingested by beef heifers.If the effects of liveweight for all animals and of milk production for cows are subtracted the withingroup coefficients of variation of amounts ingested were : — 6.6% for dairy cows, -9.1 % for dairy heifers, -7.9% for beef heifers. Levels of grass intake, expressed in g of DMlkg W J ,7 5 , in sheep (QIM) as related to cattle (OIVL, QIGL, QIGV) were the following : dairy cows dairy heifers beef heifers On account of these results, the levels of reference grass intake were the following : -

No abstract

SummaryTo test the applicability of faecal NIRS to real conditions, an experimental approach was undertaken across several representative dairy farms (N = 30) located ‘La Réunion’ island. From an ongoing survey, this approach consists to characterize the nutritional value of all feeds (grazed fresh forage, hay, silages and supplementary feeds) offered to the lactating herds, and to predict ingested diet from faecal NIRS models previously developed on a large experimental sheep faeces reference data-base.The methodological objective was to evaluate if such a spectral database could be a useful reference to estimate dairy cow total dry matter intake and diet quality, and so predict the grazed grass intake with reasonable accuracy. According to preliminary results, the NIRS estimated total intake varied between 13.7 and 19 kg DM/day and in vivo organic matter digestibility ranged from 51.7 to 74.8 % with an averaged value of 66 %. The estimated grass intake varied between 0 to nearly 10 kg DM/d. On a spectral basis, dairy cows faeces were quite different from the sheep faeces reference database, with an averaged standardised distance (H) upper of 3.0 (H = 9.1; Hmin = 2.08 – Hmax = 19.22) but predicted intake appeared valid. Indeed, according to the feeding value of diets and lactating cow requirements, the NIRS predicted total intakes were well correlated to the level of milk production. Moreover, for four particular situations, the fresh grass was cut, distributed at the trough and total intake really measured. The correlation between predicted and measured values was high with R2 = 0.94 and standard error of regression = 0.469 kg DM/d. These initial results appear quite encouraging, although the methodology is still exploratory and needs to be validated across a larger set of data. As a low cost and rapid prediction technique, NIRS appears to be a potential methodology that could find many useful developments in the improvement of the knowledge of forage use in tropical conditions.