Effects of stocking rate, supplementation, genotype and their interactions on grazing dairy systems: a review

Abstract

The main effects of, and the interactions between, stocking rate (SR), supplementation and genotype on dry matter (DM) intake, herbage utilisation, milk production and profitability of grazing dairy systems have been reviewed. The SR determines the average herbage allowance (HA) per cow and therefore has a major effect on herbage intake (HI) and on the productivity of grazing dairy systems. In this review, the effect of HA on HI is presented separately for two groups of studies: those that measured allowance at ground level and those that measured allowance at a cutting height of 3Á5 cm above ground level. HI and milk yield per hectare usually increase as SR increases. However, there is generally an associated reduction in HI and milk yield per cow because of the decrease in average HA at a higher SR. The dual objectives of adequate level of feeding per cow and high herbage utilisation per hectare can be achieved through the inclusion of supplements. The milk response to supplements depends mainly on the size of the relative energy deficit between potential energy demand and actual energy supply. The relative energy deficit determines both energy partitioning within the cow and substitution rate. The relative energy deficit is increased by either a high demand for energy within the cow or by a deficit of dietary energy available to meet the demand. Cows of different genotype differ in their potential for milk yield. Cows with high genetic potential for milk yield undergo higher relative energy deficits under grazing dairy systems, resulting in lower substitution rates, higher milk responses to supplements, but also lower body condition score, which, in turn, leads to lower reproductive performance. Whole-farm experiments in many countries have demonstrated that the inclusion of supplements, with a concomitant increase in SR, can have synergistic effects in improving the productivity of grazing dairy systems. Overall, the level of supplementation required per cow and the optimum SR depend on the genetic potential of the cow, the size of the responses to supplement, the value of milk and the costs of feeding supplements.

Managing variations in dairy cow nutrient supply under grazing

“…When considering PM and PA above 4 to 5 only, and due to the high PM below 4 to 5 cm (i.e. 2.0 to 2.5 t DM/ha), the plateau is reached at a PA of 20 to 25 kg DM/cow per day (Baudracco et al, 2010;Delagarde et al, 2011b). At this level of PA, grazing conditions are not limiting for PI, and intake can be considered equal to voluntary intake indoors.…”

“…Therefore, solutions must focus on the way to increase nutrient intake. Supplementation with concentrates The effects of feeding supplement on grazing dairy cow performance has been reviewed extensively (Peyraud and Delaby, 2001;Baudracco et al, 2010). In high genetic merit Holstein cows, efficient response of 1 kg of milk/kg of concentrate is achieved up to a concentrate supplementation level of 6 kg/day.…”

Holstein-Friesian milk performance in organic farming in North Spain: Comparison with other systems and breeds

“…In parallel, this selection process has resulted in reduced reproductive efficiency, extended calving intervals, increased health problems, increased culling rates, and decreased productive life (González-Recio et al, 2006;Bluhm, 2009) especially when these highly selected cows are out of intensive nutritional and environmental management systems. The most notable exception to the high-producer HolsteinFriesian genetic selection was carried out in Australia and New Zealand, countries with seasonal, site adapted, and pasture-based milk production systems (Macdonald et al, 2008;Baudracco et al, 2010Baudracco et al, , 2011 which are closer to the organic principles.…”

Predicting grass dry matter intake, milk yield and milk fat and protein yield of spring calving grazing dairy cows during the grazing season

“…A large response is achieved only if the performance of the cow is severely limited by lack of feed (Holmes and Mathews, 2001). Factors that increase the energy deficit decrease the substitution rate and increase the MY and MSY response to concentrate (Baudracco et al, 2010). Delaby et al (2001) found an MY response to concentrate in mid-lactation of 1.04 kg per kg DM concentrate consumed which was a large response.…”

“…This was observed in the current study where the lowest MY and MSY response occurred in SP. The MY and MSY response to concentrate depends largely on the size of the energy deficit between the potential energy demand and the actual energy supplied by the feed consumed (Baudracco et al, 2010). A large response is achieved only if the performance of the cow is severely limited by lack of feed (Holmes and Mathews, 2001).…”