Feed intake, in vivo digestibility and protein utilization of grass, red clover and maize silages in sheep

Sheep in Sweden are usually fed grass/clover forage supplemented with concentrate during the winter season. Red clover forage fed to ruminants has shown to increase dry matter (DM) intake and give a lower in vivo DM digestibility compared to grass forage. Whole-crop maize silage is increasing in use in Sweden and can complement grass silage and grass/red clover silage or replace grain concentrate due to high starch content. Maize has shown to give slightly higher live weight and carcass gain in ruminants when fed separately compared to a mix with grass/red clover silage. The intake and digestibility of silage in sheep is mostly affected by the fibre digestibility. Also, time of harvest affects intake and digestibility of the silages as advancing maturity increases the proportion of less digestible fibre where neutral detergent fibre (NDF) affects the intake negatively. In addition, well-preserved silage affects the intake and digestibility positively. To combine different feedstuffs into a balanced diet, the digestibility, nutrient content and utilization ability by the sheep of each individual feedstuff must be known. Then different forages can be combined and complemented with the right amount of concentrates to increase the production in growth or milk per feed unit, which gives decreased emissions of nitrogen (N). The aim of this study was to investigate feed intake, in vivo digestibility and protein utilization of silages fed to rams with or without protein supplementation. The relative differences between the forages are applicable to other ruminants and contribute to improved feed formulations. The silages used were whole-crop maize harvested at the dough (28 % DM) and the dent (38 % DM) stage of maturity, grass (31 % DM) and red clover/grass (32 % DM) ensiled with or without microbial inoculant. Ten rams were divided into duplicated 5 x 5 Latin squares with five rams (one treatment to each ram) and five periods in each square. One of the groups was supplemented with rapeseed meal. Each period was four weeks long and divided into sub periods with ad libitum and 80 % of ad libitum intake of silages. When the five periods were completed, all rams had been fed the five different silages. The live weight (LW), body condition score and feed intake were continuously registered during the experiment. Samples of feed, refusals, urine and faeces were collected during the four last days in each period and sent to analysis of fermentation quality and nutrient content in silage and nutrient contents in faeces and nitrogen compounds in urine. Supplementation of rapeseed meal increased silage intake of all nutrients, crude protein (CP) digestibility, urea and total N in urine. However, N in faeces in % of N intake was lower when supplementation was used. Grass and red clover silages gave generally higher intakes of DM and NDF than maize silage. Grass silage generally gave higher digestibility of DM, organic matter (OM), NDF and acid detergent fibre (ADF) than the red clover and maize silages. Furthermore, grass silage had the highest excretions of allantoin, purine derivatives (PD) and hippuric acid in urine. Red clover silage gave the highest intakes of ADF and CP, similar CP digestibility to grass silage, the highest N and urea excretion but the lowest hippuric acid excretion in urine. Early harvested maize silage had lower DM intake than the grass and red clover silages and both maize silages had the lowest intakes of CP, NDF and ADF. Late harvested maize silage had lower digestibility of DM, OM, CP, NDF and ADF than grass and red clover silages. The excretion of urea was lowest for the maize silages. There was no effect of inoculant addition to red clover silages and no effect of time of harvest of maize silage on feed intake, in vivo digestibility or protein utilization by the rams. The LW in rams were not affected by silage diet, but by supplementation of rapeseed meal, giving higher LW loss at 80 % of ad libitum feed intake compared to the un-supplemented group. In conclusion, grass silage is suitable forage for optimizing diets to ruminants as it had the highest nutrient digestibility and microbial protein efficiency. Red clover silage is suitable when balancing the protein concentration while maize silage can give a higher energy concentration in the diet for growth and production. Red clover and maize silage can preferably be combined in a diet because of the high protein content in red clover silage and the high energy content in maize silage.