Effect of replacing organic grass-clover silage from primary growth with regrowth on feed intake and milk yield of dairy cows

Abstract

Under Norwegian conditions diets based on primary growth silage (PG) typically increase milk yield compared to silage prepared from the regrowth (RG). Organic PG, dominated by immature grasses, are often high in energy and low in CP, whereas the opposite is the case for organic RG harvests, dominated by clover. Here, we tested the hypotheses that increasing proportions of RG will reduce the total supply of metabolizable energy, but increase the CP-intake, and that there is a dietary optimal mix of PG and RG to meet requirements for optimal milk production. Sixteen Norwegian Red cows were used in an experiment designed with four balanced 4 × 4 Latin squares with 21-days periods to evaluate the effect of incremental replacement of PG with RG on feed intake, nutrient digestion and milk production. Silages were prepared from PG and RG of an organically managed grassland. Treatments comprised silages fed ad libitum with RG replacing PG in ratios of 0, 0.33, 0.67 and 1 on DM basis. Additionally concentrate was offered with 8 kg for pluriparous and 7 kg for primiparous cows. The PG had higher contents metabolizable energy (ME), potentially degradable neutral detergent fiber (NDF) and water soluble carbohydrates, while RG contained more crude protein (CP) and indigestible NDF. The already mentioned characteristics led to higher intakes of DM, organic matter, NDF and ME, and lower intakes of CP and indigestible NDF with increasing proportions of PG in the diet. Milk yield tended to be higher when PG and RG were offered as a mixture than when fed alone. The milk fat concentration decreased linearly with increasing proportions of RG proportion, while protein concentration was unaffected by diet. This led to a similar production of energy corrected milk among cows fed diets containing PG while cows fed pure RG diet produced 0.9 kg less daily. Silage energy concentration and energy intake influenced milk production more than CP supply.

Modelling feed intake and milk yield responses to different grass ley harvesting strategies

“…Milk fat concentration in cows fed diets containing PG silage tended to be higher than in cows fed RG silage, which is in agreement with Kuoppala et al () and Naadland et al (). This could be mainly related to the higher D ‐value of PG than RG silage (692 vs. 660 g/kg DM), since rumen fermentation pattern is higher in butyrate when cows are fed more digestible silages (Rinne et al, ).…”

“…The concentrations of NDF and silage lactic acid are other important factors influencing milk fat concentration (Beauchemin, ; Huhtanen et al, ), but the differences between PG and RG silage were rather small in the present data set. Higher milk protein concentration in cows fed PG silage than RG silage is in line with the results of earlier studies (Khalili et al, ; Kuoppala et al, ; Naadland et al, ; Peoples & Gordon, ). It was mainly attributable to the higher ME concentration (11.1 vs. 10.6 MJ/kg DM) in PG silage and greater dietary MEI (241 vs. 224 MJ/day) in cows fed PG silage.…”

“…The difference in MEI estimated from DOM intake (16 MJ ME/kg DOM) between PG and RG silage was 4–5 MJ/day smaller than when estimated from feeding values at maintenance. The ME utilization efficiency was poorer in cows fed PG silage than RG silage, which is in line with Khalili et al () and Naadland, Sternshamn, and Randby (). However, in studies by Peoples and Gordon (), Heikkilä et al () and Kuoppala et al (), the lower milk production potential of RG silage was due to reduced feed intake, with no difference in feed utilization efficiency.…”

Effect of organic grass-clover silage on fiber digestion in dairy cows

“…The RG contained 29% timothy, 14% meadow fescue, 5% smooth meadow grass, 6% couch grass (Elytrigia repens L.) and 5% other species including herbs. A detailed description of silage production was reported in Naadland et al (2015). Experimental treatments comprised diets with replacement of PG with RG silage in the proportions 0, 0.33, 0.67 and 1 (treatments D1, D2, D3 and D4, respectively) on DM basis.…”

“…All samples were pooled across sampling times to provide one sample per cow per period. Chemical analyses of feeds are described in detail in Naadland et al (2015). The same methods were used to assess chemical composition of digesta and fecal samples.…”