The effect of crop maturity on the nutritional value of maize silage for lactating dairy cows 3. Food intake and milk production

Fifty-five multiparous Holstein-Friesian cows were used in a 20-week contin uous design study to determine the effect of maize silage maturity on food intake and milk production. Forage maize (cv. Hudson) was harvested and ens iled at target dry matter (DM) contents of 230 (T23), 280 (T28), 330 (T33) and 380 (T38) g per kg fresh weight (FW). The mean values for volatile-corr ected DM (VCDM), starch, neutral-detergent fibre (NDF), crude protein and p redicted metabolizable energy (ME) content of the four maize silages were 2 26, 290, 302 and 390 g/kg FW, 114, 274, 309 and 354 g/kg VCDM, 574, 447, 43 1 and 448 g/kg VCDM, 96, 80, 74 and 75 g/kg VCDM and 10.3, 11.5, 11.6 and 1 1.2 MJ/kg DM, respectively Grass silage containing 296 g VCDM per kg FW was produced from the primary growth of a perennial ryegrass sward. At week 3 of lactation cows were allocated to one of five forage treatments offered a d libitum. The forage treatments were either grass silage alone (TGS) or a 3:1 DM ratio of maize and grass silage designated as T23, T28, T33 and T38. All cows also received 8.7 kg DM per day of a dairy concentrate. Forage VC DM intake for TGS was lower (P < 0.001) than for T23 to T38. Increasing mai ze silage Dill content from 226 (T23) to 290 (T28) g/kg increased (P < 0.05 ) forage VCDM intake from 10.9 to 13.3 kg/day but a further increase to 390 (T38) g/kg tended to reduce VCDM intake. When compared with TGS, the inclu sion of maize silage increased milk yield from 28.0 kg/day to 29.4, 32.7, 3 3.0 and 30.8 kg/day for T23 to T38, respectively, the increases being signi ficant for T28 to T38. However, milk yield was reduced (P < 0.05) when the DM content of the maize silage increased from 302 to 390 g/kg. Increasing m aize silage DM content from T23 to T33 reduced (P < 0.05) milkfat content f rom 45.8 to 41.8 g/kg, which was also lower (P < 0.05) than for TGS. The in clusion of maize silage increased fat yield with a significant difference ( P < 0.05) between TGS and T28. The inclusion of maize silage increased milk protein content (P < 0.05) Ind protein yield (P < 0.001) when compared wit h TGS. While increasing maize silage maturity did not affect (P > 0.05) mil k protein content, protein yield was higher (P < 0.05) for the two intermed iate DM contents. There were no treatment effects on body condition score. It is concluded that the changes in composition of maize si,rage with incre asing maturity, which are associated with increased starch and reduced NDF content, resulted in large increases in food intake and yield of milk and p rotein as crops matured from T23 to T33. However, when crop maturity increa sed further to T38 there was a tendency for Dh I intake and yield of milk a nd protein to decline.