Feed intake and energy utilization in dairy cows of different breeds

anglais. Improvement of nutrition of dairy cows and improvement of the genetic capacity for milk production aim to improve the efficiency of converting feed into milk. This efficiency can be expressed as the ratio between energy in milk and Net Energy intake (defined as the biological efficiency) or as the difference between returns from milk and feed costs (defined as the economic efficiency). In these two definitions of efficiency the relationship between feed intake and milk production is very important. Little is known about genetic differences in feed intake and feed efficiency and a possible interaction with diet composition. Genetic differences among cows may be reflected in differences between groups of cows of different breeds, which are selected with a different breeding goal. Differences in diet composition are reflected in complete diets, which differ in the ratio between concentrates and roughages.The aim of this thesis is to describe differences between dairy breeds in feed intake and in partition of Net Energy between milk production, maintenance and gain in different circumstances: different parities, different parts of lactation, feeding ad libitum complete diets which differ in roughage content and treatment with different dosages of bovine somatotropin. Relationships between feed intake and milk production, maintenance and gain are presented in the different circumstances. Possibilities to manipulate feed intake and energy utilization in dairy cattle are outlined.The study is based on feed intake experiments with cows of four breeds: the Jersey, the Holstein Friesian (HF), the Dutch Friesian (DF) and the Dutch Red and White (DRW). In four experiments the cows were fed ad libitum two completely mixed diets with respectively 0 and 50 per cent concentrates. In a fifth experiment cows of different breeds were treated with bovine somatotropin (BST), while fed ad libitum a diet with 50 per cent concentrates. In all trials the roughage was a mixture of corn silage and of high quality grass silage or artificially dried grass.In Chapter 2 an experiment with HF, DF and DRW heifers is described. From 2 months before the first calving until 10 months of lactation they were fed ad libitum a complete diet with roughages or a complete diet of the similar roughages with 50 per cent concentrates on a dry matter basis. In the experimental period of 52 weeks the breeds differed significantly in energy intake, milk energy production and in biological efficiency. In the HF, DF and DRW heifers these figures were respectively: 32601, 30884 and 30581 MJ NE in feed; 16553, 15086 and 14814 MJ energy in milk and 51, 49 and 48 per cent. Despite large differences in feed energy intake and milk energy production between the concentrates (C) and roughage (R) diet (8500 MJ NE and 4246 MJ) no significant interaction was found between breed and diet composition for any of the studied characteristics. The biological efficiency for milk production was equal for the C and R diet: 49 per cent. Body weight gain of the concentrates group was 59 kg higher than that of the roughage group.In Chapter 3 the results of a feed intake study with HF, DF and DRW cows in second lactation are presented and discussed. These cows participated in the study described in Chapter 2 on the same diets. In this experiment their feed intake was measured from two months before the second calving until 10 months of the second lactation. For none of the studied traits a significant interaction between breed and diet composition was found: differences between breeds were independent of diet composition. In the HF, DF and DRW cows feed energy intake was 35052, 35182 and 32015 MJ NE respectively; milk energy was 18700, 15475 and 15548 MJ respectively and biological efficiency 55, 44 and 48 per cent respectively. Between the concentrates and the roughage diet the difference in feed energy intake was 6210 MJ NE, in milk energy production 4423 MJ and in biological efficiency on an absolute basis 4 per cent. The increase in milk yield from first to second lactation was significantly higher in the HF cows than in the DF and DRW cows. The body weight gain of the concentrates group in second lactation was much less than in first lactation.Chapter 4 reports on an experiment with Jersey heifers and a control group of HF + DF + DRW heifers, which were fed a complete diet of roughages or a complete diet of the similar roughages and 50 per cent concentrates on a dry matter basis in the first 39 weeks of lactation. Significant interactions between breed and diet composition were found for feed energy intake, milk yield, fat percentage in milk, milk protein yield and milk energy production. For these traits the differences between the breeds were dependent of the diet composition. Mean differences between the Jersey and the HF + DF + DRW heifers on the C diet and on the R diet (in parentheses) were: -6527 (-4319) MJ NE for feed energy intake; -1791 (- 991) kg for milk yield; 2.31 (1.84) for fat percentage; -5 (-16) kg for protein yield and -2533 (-898) MJ for milk energy production. These breed x diet interactions might be caused by a higher feed intake capacity of the Jersey heifers compared to the HF + DF + DRW heifers and the relatively higher need of Jerseys for lipogenic precursors and a lower need for aminogenic and glucogenic precursors for milk synthesis, which have better been provided for on the roughage diet. The biological efficiency for milk production was 65 per cent for the Jersey heifers on the roughage diet, 59 per cent for the Jersey heifers on the concentrates diet, 56 per cent for the HF + DF + DRW heifers on the R diet and 55 per cent for the HF + DF + DRW heifers on the C diet.In Chapter 5 a further study with Jersey cows and a control group of HF + DF + DRW cows is described. After their third calving these cows, which participated in the former study as a heifer, were fed the same diets as in the previous described study. Again body weight, milk production and feed intake were recorded in the first 39 weeks of lactation. Only for fat percentage of milk a significant interaction between breed and diet composition was found. Mean differences between the Jersey and the HF + DF + DRW cows on the C diet and on the R diet (in parentheses) were -6460 (-5162) MJ NE for feed energy intake; -2560 (-1707) kg for milk yield; 2.82 (2.38) for fat percentage in the milk; - 55 (-26) kg for protein yield and -3241 (-1112) MJ for milk energy production. The increase in Net Energy intake and milk yield from first to third lactation was for the Jerseys and the HF + W + DRW cows on the C diet 25 and 24 per cent, respectively and on the R diet 48 and 51 per cent respectively. The biological efficiency for milk production was 69 per cent for the Jerseys on the roughage diet, 57 per cent for the Jerseys on the C diet, 61 per cent for the HF + DF + DRW cows on the R diet and 56 per cent for the HF + DF + DRW cows on the C diet.In Chapter 6 the effect of parity on feed intake and feed efficiency are established in weeks I - 39 of lactation. For this purpose 265 lactations of 159 cows out of the experiments described in the Chapters 2 - 5 were available. Unequal variances among breeds in the different parity x diet groups and some differences in ranking of the breeds caused a significant three-way interaction parity x breed x diet. In general, the differences between the C and R diet groups in feed intake and milk production decreased with increasing parity. Biological efficiency was not affected by parity. Economic efficiency increased in higher parities, which was most pronounced on the R diet. The presence of data from cows in two lactations facilitated calculations of repeatabilities for the studied traits. Repeatabilities for fat concentration (0.75), protein concentration (0.68) and average body weight (0,69) were high. Repeatabilities for dry matter intake (0.39), milk yield (0.47), biological efficiency (0.46), economic efficiency (0.37) and gain during lactation (0.27) were lower. An attempt to detect possible differences between parities, diets and breeds in Net Energy requirements for milk production, maintenance and gain was not successful. A multiple regression of Net Energy intake on milk energy, metabolic weight and gain yielded unrealistic coefficients of regression, which might be due to measurement errors for the independent variables and to relationships between these variables.Chapter 7 is a description of an experiment with Jersey, Friesian and Dutch Red and White cows, which were treated from week 13 to week 36 of lactation with recombinantly derived bovine somatotropin in a sustained delivery vehicle. After an 84 days pretreatment period four treatments were used: an untreated control and three different levels of somatotropin administered once every 28-days in a sustained delivery vehicle by subcutaneous injection. From weeks 1 - 36 the cows were fed ad libitum a complete diet of 50 per cent concentrates and 50 per cent roughage, No significant interaction between breeds and treatment was detected. In the three breeds the 640 mg-dosage gave optimum results: an increase in daily milk yield of 3.3 kg was found and fat percentage increased by 0.24 per cent. The plasma levels of 3-hydroxybutyrate tended to be higher in treated cows and fat percentage of their milk showed large variations within a four weeks period, which both indicate the involvement of adipose tissues in the response in milk fat production after BST-treatment. This is one of the reasons to study effects of exogenous bovine somatotropin over more than one lactation. Cows with a higher milk yield in the pretreatment period, showed a slightly lower increase in milk production after treatment with somatotropin than cows with a lower milk yield in the pretreatment period.Chapter 8 is a general discussion, which founds the conclusions of this thesis. Between breeds differences exist in voluntary feed intake, which are related to differences in their feed requirements. Jerseys have a much lower voluntary feed intake than Holstein Friesians, Dutch Friesians and Dutch Red and Whites. However, the feed intake capacity (feed intake in relation to body weight) is higher in the Jerseys. When Jerseys are involved in a breed comparison, the differences between the breeds depend on the concentrates level of the diet. Jerseys have a different ratio between fat, protein and lactose in the milk compared to the other breeds, which might be an explanation for the breed x diet interaction, when Jerseys are involved in a comparison with larger breeds. Differences in feed intake capacity between breeds are associated with differences in body conformation and are negatively related to slaughter quality traits. Feed intake capacity increases with parity, especially on a roughage diet. The Jerseys and Holstein Friesians have a higher biological and economic efficiency for milk production than Dutch Friesians and Dutch Red and Whites, because of a higher ratio between milk energy production and maintenance requirements. Stage of lactation has a considerable effect on biological efficiency. Biological efficiency for milk production is slightly lower on a concentrates diet than on a roughage diet. Differences between breeds in biological efficiency are more pronounced on the roughage diet. Differences between breeds in economic efficiency are dependent on the diet. The profitability of concentrates feeding decreases with increasing parity, especially in the dairy breeds. The total economic efficiency of a breed on farm level is mainly determined by prices for milk, beef and feed and by market restrictions. Biological and economic efficiency can be improved by a higher milk yield. Biological efficiency is not affected by differences in dry matter intake or body weight. Feed intake of dairy cows is greatly influenced by the ratio between concentrates and roughage in the diet and to a limited extent by treatment with bovine somatotropin. The ratio between concentrates and roughage in the diet has a minor effect on feed efficiency. Administration of bovine somatotropin and selection for milk yield has a positive effect on feed efficiency by diluting maintenance costs per kg milk.

néerlandais; flamand. Op basis van voeropnameproeven met 4 rassen: de Jersey, de Holstein Friesian, de Nederlandse zwartbonte en de Nederlandse roodbonte (MRIJ), worden verschillen tussen melkveerassen in voeropname beschreven en in de verdeling van de netto-energie in het voer over melkproduktie, onderhoud en groei. De effecten van leeftijd (pariteit), lactatiestadium, de verhouding tussen ruwvoer en krachtvoer in het rantsoen en de effecten van behandeling met verschillende doses bovine somatotropine op deze verschillen zijn vastgelegd. De mogelijkheden om de voeropname en de efficientie van de omzetting van voer in melk te veranderen worden besproken