Responses to grain feeding by grazing dairy cows

Abstract

Summary. Two experiments were conducted on feeding grain supplements to dairy cows during summer. In experiment 1, dairy cows in mid–late lactation were offered one of 2 pasture allowances (about 20 and 40 kg DM/cow.day) with and without a supplement of a grain mix (5 kg of a 70 : 30 mixture of barley and lupins). This experiment was conducted twice over 2 consecutive summer–autumn periods (years 1 and 2). Milk yields were higher at the high pasture allowance and with grain feeding. The marginal response to grain feeding (kg milk/kg grain DM consumed) was 0.7 at both pasture allowances in year 1, and 1.1 and 0.8 at the low and high pasture allowance, respectively, in year 2. Diet had no significant effect on milk composition. Pasture intake was reduced by supplementary feeding and the level of substitution depended on pasture allowance. The alkane-based and sward sampling techniques were used to estimate pasture intake and diet digestibility. Estimates of pasture substitution, based on measurements made with the alkane technique, were 0.3 and 0.6 kg DM reduction in pasture/kg DM grain consumed at the low and high pasture allowance, respectively, in both years. In year 1, the pasture substitution measured with the pasture difference method was 1 kg pasture DM/kg grain DM at both pasture allowances. In year 2, estimates of substitution calculated using the pasture difference method were 0.2 and 0.5 kg pasture DM/kg grain DM at the low and high pasture allowance respectively. In the second experiment (year 3), the effects of level of feeding barley on pasture intake, diet digestibility and milk production were measured during summer. The 4 levels of grain consumed were 0, 1.8, 3.4 and 6.7 kg barley DM/cow. day. Higher grain intake resulted in higher milk yield, higher protein concentration and yields of fat, protein and lactose. Milk yield responses per kilogram of barley diminished from 1.6 at the low barley intake to 0.8 kg milk/kg barley DM at the highest barley intake. It is suggested that higher levels of substitution and a potentially less efficient use of grain contributed to the poorer production responses at higher levels of grain feeding.

Nutritional Strategies to Improve Nitrogen use Efficiency by Grazing Dairy Cows

“…Cows consuming only pasture had a NUE of 21.0 ± 6.1% while supplemented grazing cows improved their NUE, storing in the milk 24.6 ± 3.8% of the ingested N, showing a positive effect of CHO supplementation on NUE (Van Vuuren et al, 1993;Berzaghi et al, 1996;Carruthers and Neil, 1997;Robaina et al, 1998;Reis and Combs, 2000;Walker et al, 2001;Bargo et al, 2002;Steinshamn et al, 2006). This improvement may be due to a decrease in CP content of the diet and to an increase of microbial protein synthesis.…”

“…This improvement may be due to a decrease in CP content of the diet and to an increase of microbial protein synthesis. However, it is important to highlight that the improvement of NUE as a response to CHO supplementation occurs mainly when the pasture has a CP content higher than 200 g kg -1 (Van Vuuren et al, 1993;Berzaghi et al, 1996;Reis and Combs, 2000;Bargo et al, 2002); whereas with a lower CP content the effects are less important (Carruthers and Neil, 1997;O'Mara et al, 1997;Robaina et al, 1998;Walker et al, 2001;Steinshamn et al, 2006). Nevertheless, the highest reported values of NUE under grazing conditions are still lower than the ones obtained with cows fed total mixed rations (TMR), indicating that despite CHO supplementation there is still the possibility to develop other strategies that could improve NUE even more under grazing conditions.…”

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

“…Robaina et al (1998) found that milk responses to grain feeding in mid to late lactation cows grazing summer pastures ranged from 0.7 to 1.5 kg of milk/kg of grain consumed, depending on HA and level of grain fed. They suggested that pasture availability and quality seem to dominate responses to concentrate feeding under pasture-based systems.…”

“…In addition, grain fed to dairy cows at levels greater than 6 kg DM/ cow per day may have detrimental effects on digestion in the rumen (Robaina et al 1998). High intakes of grain may reduce the digestion of forage and increase the amount of starch escaping digestion (Stockdale et al 1987).…”

“…Several reviews and experiments suggested 4Á5 kg DM/ cow per day as the maximum amount of concentrate fed before milk response declined (Kellaway & Porta 1993;Robaina et al 1998;Walker et al 2001). For each additional kg DM of concentrate eaten, substitution increased by 0.03 kg DM/kg DM (Stockdale 2000b).…”