Dairy cows grazing an alpine pasture: effect of pattern of supplement allocation on herbage intake, body condition, milk yield and coagulation properties

Anim. Res. Dairy cows grazing an alpine pasture: effect of pattern of supplement allocation on herbage intake, body condition, milk yield and coagulation properties 0 Istituto Agrario , via E. Mach 2, 38010 S. Michele all'Adige (TN) , Italy 1 Dipartimento di Scienze della Produzione Animale, Università di Udine , via S. Mauro 2, 33010 Pagnacco (UD) , Italy - The effect of two patterns of concentrate allocation were studied on twenty-eight Italian Brown cows (initial milk yield, 19.4 kg·d-1) grazing an alpine pasture. One group was supplemented at a flat rate, based on the initial milk production (Flat Supplement, FS), while the second was supplemented at a declining rate, according to the decline of lactation (Declining Supplement, DS). During an 8-week period in July and August, the cows were moved onto 8 successive sectors, ensuring a daily herbage allowance of 20 kg of dry matter per cow. The crude protein content of the herbage decreased from 19.5% at the beginning to 12.4% at the end, while the fibre fractions showed an opposite trend. The DS group showed a slightly higher, not significant, herbage intake (10.9 vs. 10.6 kg OM·d-1). BCS changes were in no case different from 0. The milk yield was positively affected by the FS (17.0 kg·d-1 vs. 15.2 kg·d-1); no difference was observed in milk composition. Coagulation properties were satisfactory without any appreciable effect of the two treatments. - dans lesquels la disponibilité en herbe était d’environ 20 kg de matière sèche par jour. La teneur en matières azotées totales de l’herbe a diminué de 19,5 % (de la matière sèche) à 12,4 % pendant l’essai, tandis que celle en fractions fibreuses a présenté une évolution inverse. Le lot DS a été caractérisé par une ingestion plus faible de concentré (3,5 kg vs. 4,5 kg de matière organique par jour) et légèrement plus élevée d’herbe (+0,3 kg MO·j–1 ; différence non significative). Les variations de la note d’état corporel n’ont pas été significativement différentes de 0. La production de lait a été augmentée avec le traitement FS (17,0 vs. 15,2 kg·j–1). La composition du lait n’a pas présenté de différences significatives. Les propriétés de coagulation du lait ont été satisfaisantes et n’ont pas été affectées par les traitements. vache laitière / pâturage / supplémentation / ingestion d’herbe / production laitière 1. INTRODUCTION The exploitation of mountain pastures by grazing with dairy cows offers advantages for the economy of many rural areas, the health of the animals and the protection of the environment, but it also poses feeding problems which are not easy to solve. The pastures, especially those located at the highest altitudes, may not be capable of meeting the nutritional requirements of the animals, increased by the movement involved and by the low temperatures. Under these conditions, there is often a fall in milk production – also related to the number of days in milk and the genetic merit of the cows [ 21, 31 ] – normally accompanied by a failure to recover body condition [ 1, 12, 22, 31 ]. In order to offset these effects, it is generally necessary to supplement with concentrates, whose benefit in terms of increased level of nutrition is conditioned by the possible reduction in the amount of herbage consumed. Much research has been conducted on dairy cows at pasture to establish the effect of the level and quality of the concentrates offered. Less research has been done on the pattern of supplement allocation [ 18 ]. The objective of this experiment, carried out on a high altitude alpine pasture, was to evaluate the effect of a flat or declining rate of concentrate supplementation on herbage intake, body condition, milk yield and quality, including coagulation properties since the milk produced in these environments is always used for cheese making. 2. MATERIALS AND METHODS 2.1. Pasture and grazing management The experiment was carried out for 8 weeks, from July 2 to August 27 on a high mountain pasture in the eastern Alps region (Malga Juribello, Province of Trento, Italy), within the “Paneveggio – Pale di S. Martino” Natural Park. The 20 ha experimental area, divided by electric fences into 8 sectors, was located at an altitude of 1800–2000 m. The pasture was mainly a Poion alpinae with the presence of high feeding value species such as Poa alpina, Phleum alpinum, Trifolium pratense, Tr. repens; the weed species were mainly Deschampsia cespitosa and Rumex alpinus. The only sort of fertiliser applied was manure. During the experimental period the pasture was utilised by weekly moving the animals into 8 sectors, starting with those located at the lowest altitude. In the pre-experimental period, the cows grazed a contiguous sector with a similar botanical composition. The sector area was calculated so as to ensure a mean daily herbage allowance per cow of 20 kg dry matter (DM). 2.2. Animals, treatments and experimental design Twenty-eight lactating Italian Brown cows (potentia (...truncated)