Material and methods formulated to ensure similar energy contents 0.90

O . Colin-Schoellen et al. Livestock Production Science 67 2000 41 –53 43

2. Material and methods formulated to ensure similar energy contents 0.90

21 UFL kg DM 1 UFL 5 1700 kcal of net energy 2.1. Experimental design and cow management for lactation Vermorel, 1988. Two trials were performed with the same ex- 2.1.2. Trial 2 perimental design and two standard treatments. In Two metabolizable protein supply levels both trials, the cows were housed in free stalls at the 21 medium 5 95, or low 5 85 g PDIE kg DM and ENSAIA experimental station in Nancy France. three levels of difference between rumen-degradable The animals were fed a total mixed ration once a day 21 energy and N PDIE 2 PDIN 5 0, 10 or 20 g kg in the morning ad libitum to which they had access DM were tested in a replicated Latin-square design continuously using electronic feed gates. Each cow 4 3 4 with four diets: medium PDIE content and was fitted with an electronic transponder with access balanced rumen fermentable energy and N diet 1, to one of the gates. All cows were milked twice daily rumen-degradable PDIN deficit of 10 g diet 2 or 20 and individual milk yields were automatically re- 21 g kg DM diet 3, and low PDIE content and corded at each milking time Isalait 2045 system, 21 rumen-degradable PDIN deficit of 10 g kg DM Boumatic. diet 4. Thirty-two Prim’Holstein cows, of which eight were primiparous, were blocked in eight Latin- 2.1.1. Trial 1 squares. All cows began experimentation on the Two metabolizable protein supply levels high 5 same day. The lactation stage at the beginning of the 21 108, or medium 5 98 g PDIE kg DM and two trial was 55 623 days and body weight was 622 levels of difference between rumen-degradable 671 kg. Mean milk yield over the 2 pre-ex- 21 energy and N PDIE 2 PDIN 5 0 or 10 g PDIN kg 21 perimental weeks was 31.2 65.9 kg day . The DM were tested in a replicated Latin-square design animals were fed a total mixed ration composed of 3 3 3 with three diets: high PDIE content and corn silage, wheat straw, soybean meal, formalde- 21 rumen-degradable PDIN deficit of 10 g kg DM, hyde-treated mixed meal, minerals and sugar beet medium PDIE content and balanced rumen ferment- pulp only for the diet with the rumen-degradable N able energy and N, and medium PDIE content and 21 deficit of 20 g PDIN kg DM. The proportions of 21 rumen-degradable PDIN deficit of 10 g kg DM. the different components of the diet were varied with Twenty four Holstein cows, of which nine were the aim of reaching optimum PDIE content and primiparous, were blocked in eight Latin-squares by rumen-degradable PDIN deficit Table 2. The diets parity, calving date, milk true protein yield, and milk were formulated to ensure similar energy contents NPN content average over two pre-experimental 21 0.90–0.92 UFL kg DM. weeks. All cows began experimentation on the same For both trials, the succession of treatments for day. The lactation stage at the beginning of the trial each cow in the first Latin square was determined was 83 637 days and body weight was 588 650 randomly. For the seven other Latin squares, the kg. Mean milk yield, fat, true protein, and NPN succession of treatments was the same as for the first contents for the two pre-experimental weeks were Latin square. Each experimental period lasted 5 21 21 30.9 65.0 kg day , 41.6 66.7 g kg , 31.1 weeks and all measurements were taken during the 21 21 62.8 g kg and 281 621 mg l , respectively. last 2 weeks of each period. The animals were fed a total mixed ration composed of corn silage, soybean meal, formaldehyde-treated mixed meal rape and soybean, 20:80, urea for the 2.2. Sampling and analysis diet with balanced contents of rumen-degradable energy and N, and minerals. The proportions of the Feed intakes and refusals for each cow were different components of the diet were varied with the measured daily for 5 days week and DM analyses aim of reaching optimum PDIE content and rumen- were carried out on a composite sample of the feed degradable PDIN deficit Table 1. The diets were offered and the refusals for each dietary treatment. 44 O . Colin-Schoellen et al. Livestock Production Science 67 2000 41 –53 Table 1 a Composition and estimated nutritive value of diets in trial 1 High PDIE content Medium PDIE content 21 PDIN deficit 5 10 g kg DM 21 No PDIN deficit PDIN deficit 5 10 g kg DM Composition of the DM Corn silage 81.7 84.5 85.1 Soybean meal 4.0 4.7 4.7 Formaldehyde treated mixed meal 12.7 8.6 8.7 Urea – 0.7 – Minerals 1.6 1.5 1.5 21 Chemical composition g kg DM CP 138 144 125 CF 157 159 160 ADF 200 207 209 NDF 374 387 389 Ash 61 59 59 b DT 0.55 0.64 0.58 a Nutritive value kg DM c UFL 0.90 0.90 0.90 d PDIN 98 97 87 d PDIE 108 98 98 e PDIA 59 48 48 a Calculated from the analyses of forage and concentrates. b DT: theoretical degradability in the rumen of the proteins of the total mixed ration. c UFL: feed unit for lactation net energy. d PDIN, PDIE: Protein digestible in the small intestine when rumen fermentable nitrogen or energy, respectively, are limiting. e PDIA: By-pass protein digestible in the small intestine. The cows were weighed on two consecutive days, Each foodstuff was sampled monthly and analyzed approximately 6 h after access to the diet, at the end chemically DM, CP, CF, ADF, NDF and ash. of the pre-experimental period, and during the last Energy and PDI values were calculated Jarrige, week of each experimental period. 1988. The percentages of cow energy and PDI require- Milk composition was determined at two consecu- ments covered were calculated from the energy and tive milkings during the first 3 weeks of each PDI supplies of the diets and from maintenance and experimental period and at four consecutive milkings milk production requirements Jarrige, 1988. The during the last 2 weeks of each experimental period. efficiency of the utilization of crude protein supplies The milk fat and true protein contents were analyzed for milk protein synthesis was estimated from the by the infrared method IRMA analyzer, Hillerød, milk protein N yield N intake ratio and milk NPN Denmark and the somatic cells were counted by yield N intake ratio. nuclear coloration Fossomatic analyzer, Hillerød, Denmark. During the last 2 weeks of each ex- perimental period, using the same samples as those 2.3. Statistical analysis used for milk composition, total N, NPN and pH- soluble N contents were determined by the Kjeldahl Individual data were tested by ANOVA using SAS method in trial 1, total N, NPN contents and milk Procedure Mixed SAS, 1996. The statistical model urea content by the Siest 1978 method, modified by took into account the effects of dietary treatment, Brun-Bellut personal communication in trial 2. The period, parity, Latin-square within parity, cow within protein trial 1 and 2 and casein N trial 1 contents Latin-square and parity, and interaction between were calculated from these measurements. dietary treatment and parity. The individual means O . Colin-Schoellen et al. Livestock Production Science 67 2000 41 –53 45 Table 2 a Composition and estimated nutritive value of diets in trial 2 Medium PDIE content Low PDIE content PDIN deficit 5 No PDIN PDIN deficit 5 PDIN deficit 5 21 10 g kg DM 21 21 deficit 10 g kg DM 20 g kg DM Composition of the DM Corn silage 77.3 83.3 72.8 87.4 Wheat straw 3.2 – – – Soybean meal 17.9 11.5 5.0 11.0 Formaldehyde treated mixed meal – 3.5 6.4 – Sugarbeet pulp – – 14.2 – Minerals 1.6 1.7 1.6 1.6 21 Chemical composition g kg DM CP 139 126 111 109 CF 171 169 173 174 ADF 198 197 173 207 NDF 389 388 339 407 Ash 64 63 63 61 b DT 0.65 0.63 0.57 0.67 a Nutritive value kg DM c UFL 0.90 0.91 0.92 0.91 d PDIN 94 86 77 72 d PDIE 96 95 97 84 e PDIA 45 44 43 33 a Calculated from the analyses of forage and concentrates. b DT: theoretical degradability in the rumen of the proteins of the total mixed ration. c UFL: feed unit for lactation net energy. d PDIN, PDIE: Protein digestible in the small intestine when rumen fermentable nitrogen or energy, respectively, are limiting. e PDIA: By-pass protein digestible in the small intestine. 21 for the last 2 weeks of each experimental period rumen-degradable PDIN deficit of 10 or 20 g kg DM, all three with a medium PDIE level. were tested for each measured variable. The effects of the metabolizable protein supply level and of the magnitude of rumen-degradable PDIN deficit were

3. Results tested by the contrast method Dagnelie, 1994. In