|dc.description.abstract||1. In a single-lactation 240-day continuous trail, 64 lactating dairy animals were used to study input-output response to complete rations. Nine first-calf heifers and seven cows were allotted by the procedure of balancing to each of the four experimental treatments. Ration treatments were: 80% lucern: 20% concentrate (ration A), 60% lucern: 40% concentrate (ration B), 40% lucern: 60% concentrate (ration C) and 20% lucern: 80% concentrate (ration D). The crude fibre percentages of rations A, B, C and D were 23,16; 19.34; 16,11 and 12.01, respectively. These rations were pelleted and fed ad lib. in addition to 9 kg of maize silage daily. A digestibility trial with four additional lactating dairy animals was carried out simultaneously.
2. With decreasing proportions of lucern, digestibility of the dry matter increased from 55,55 to 65,33 per cent (P<0,05). Increasing the proportion of concentrates in the ration led to an increased concentration of metabolizable energy (P<0,05). The digestible protein in the rations varied very slightly (P>0,05).
3. Changes in body mass of cows and first-calf heifers due to ration treatment were non-significant (P>0,05). Age was the most important factor influencing body mass variations of experimental animals; differences between cows and first-calf heifers being highly significant (P<0,01) in favour of the cows. The individual mean body mass gain of the first-calf heifers during their first lactation was 80,4 kg compared to 9,9 kg of the cows in their second and later lactations.
4. There were non-significant (P>0,05) differences, due to ration treatment, in the daily amount of actual milk, 4% fat corrected milk and solids corrected milk produced by cows. Although first-calf heifers on ration D produced 19,3 to 27,0 percent more actual milk, 14,0 to 23,0 per cent more 4% fat corrected milk and 16,3 to 22,9 per cent more solids corrected milk than heifers on either the A, B or C rations, these differences were non-significant.
5. Cows on ration A, B and C produced more (P<0,05) milk, 4% fat corrected milk and solids corrected milk, during each stage of lactation, than the first-calf heifers. Cows fed ration D showed a significantly (P<0,05) higher production than heifers, during the third to fifth month of lactation and a non-significant difference during the sixth to tenth month.
6. Small non-significant (P>0,05) differences occurred in the mean solids-no-fat content of milk. Solids-not-fat content of milk produced by cows ranged from 8,69 to 9,02 per cent and from 8,90 to 9,16 per cent in the case of first-calf heifers. The milk produced by first-calf heifers had a significantly higher (P<0,01) solids-not-fat content than cows during all stages of lactation, irrespective of ration treatment.
7. Milk fat was non-significantly affected by ration treatment. Decreasing lucern content in the ration was accompanied by a decrease in the fat percentage of milk produced by cows (0,3) and by heifers (0,29).
8. The dry matter and gross energy consumption by cows tended to decrease as the dry matter digestibility of the ration increased, differences being non-significant. Similarly as the metabolizable energy concentration increased (increasing with a decreasing proportion of lucern) the voluntary intake by cows tended to decrease. Metabolizable energy intake between ration treatments was very constant and was related to the mean daily yield of the cows.
The intake of dry matter and gross energy by first-calf heifers remained more or less the same for all rations (P>0,05). However, as the dry matter digestibility of the ration increased the metabolizable energy consumption by heifers tended to increase, differences being non-significant.
9. Cows consumed significantly (P<0,01) more dry matter, gross energy and metabolizable energy during certain stages of lactation than first-calf heifers, irrespective of ration treatment. In the case of cows the efficiency of metabolizable energy utilization for milk production increased as the lucern portion in the ration increased, differences non-significant. A very similar tendency was noticed with the first-calf heifers. Irrespective of ration treatment cows produced milk more efficiently (P<0,05) during the third and fourth month of lactation than during the later months. The effect of stage of lactation on efficiency of use of metabolizable energy for milk production by heifers was less pronounced than that obtained with cows, but the differences were non-significant.
10. Irrespective of treatment the cows produced milk more efficiently (P<0,01) durng the third and fourth month of lactation than the first-calf heifers. During the fifth, sixth and seventh month of lactation efficiency of milk production by cows and heifers was very similar. During the eighth and ninth month of lactation heifers were more efficient than the cows.
11. In terms of marketing fresh milk the profit margins over cost of feed was 5,6; 6,0; 6,1 and 6,2 c per litre when cows were fed rations A, B, C and D respectively. The profit margins for first-calf heifers were 4,8; 4,7; 4,8 and 6,0 c per litre for the same rations. Reproduction of cows and first-calf heifers was non-significantly affected by ration treatment.
12. None of the experimental rations caused bloat-, digestive- or general stiffness problems. Seventeen cases of mastitis occurred during the course of three years and seven months.
13. In four switchback trials with 16 lactating dairy animals the pelleted experimental rations were compared with otherwise identical non-pelleted rations (lucern portion being chaffed in 2,5 cm lengths). The method of preparing the rations by either pelleting or non-pelleting did not appreciably influence the dry matter consumption (g DM/W kg 0,75), daily amounts of actual milk produced, solids corrected milk and composition of milk. However, animals receiving ration D in a non-pelleted form, produced significantly (P<0,05) more solids corrected milk and total solids in milk than animals fed the corresponding pelleted ration.||en_ZA