A 3-year experiment on milk produclion systems was set up in 1989 to investigate the effect of calving date and stocking rate on the performance of spring-calving dairy cows. An early-calving herd (System A) with a mean calving date of 23 January and stocked at 2-9 cows per hectare was compared with two later calving herds (Systems B and C) with a mean calving date of 15 March. System B had a similar stocking rate to System A (2'9 cows ha"'), while System C had a stocking rate of 26 cows ha"'. The average lactation yields (kg) over the three years were as follows: 5872, 5444 and 5584 (milk) 210. 204 and 215 (fat). 187, 184 and 189 (protein) and 261, 245 and 250 (lactose) for Systems A. B and C respectively. The average milk composition (g kg-') was; 36.0. 37-6 and 38-7 (fat), 31-9, 33-7 and 33-8 (protein) and 44-5. 45-1 and 44-8 (lactose) for Systems A. B and C respectively. Delaying calving date to coincide with the beginning of the grass-growing season (System B compared with System A) reduced milk yield per cow significantly (P<005) in all three years of the experiment.

A total of 48 high genetic merit (HM) and 48 medium merit (MM) cows, each given a low (LC), medium (MC), or high (HC) level of concentrate supplementation, were used in a split-plot design experiment, which was run in three consecutive years, to evaluate animal production responses. Individual cow intakes were estimated twice each year while at pasture; measurement period 1 (MP1) was in May/June, and measurement period 2 (MP2) was in early September, corresponding on average to d 110 and 200 of lactation, respectively. In MP1, cows were offered 0 (LC), 3 (MC), and 6 kg (HC), whereas in MP2 the levels were 0 (LC), 0 (MC), and 4 kg (HC) of concentrate daily. Genotype had a significant effect on all milk production parameters in MP1 and MP2. The HM cows had the highest yield of milk, fat, protein, and lactose, whereas the MM cows had the highest milk fat, protein, and lactose concentrations. The HM cows had significantly higher grass dry matter intake (GDMI) estimates. In MP1, the average responses, per kg concentrate dry matter, was +1.10 kg of milk, +0.038 kg of protein, +0.032 kg of fat. The corresponding values in MP2 were +0.94 kg of milk, +0.037 kg of protein, and +0.025 kg of fat. The response to concentrate was linear and independent of preexperimental milk yield. In MP1, the partial regression coefficients relating daily GDMI to an increase in 1 kg of preexperimental milk yield (PMY), preexperimental BW (PBW), and concentrate intake (CI) were 0.123, 0.006, and -0.54, respectively, whereas the corresponding values in MP2 were 0.190,0.007, and-0.444, respectively. This study indicates that with high yielding dairy cows, on gras only GDMI of 17 kg of supporting milk yield of 30-kg/d is achievable. In this scenario, concentrate supplementation will result in lower substitution rates, and higher milk yield response than previously published with lower yielding cows.

Milk was collected from three spring-calving herds, on different daily herbage allowances (DHA) of perennial rye-grass (16, 20 or 24 kg dry matter (DM)/cow for a 17 week period. On five occasions, at weekly intervals in the middle of the period, the three different milks were converted into low-moisture part-skim Mozzarella cheese. Increasing the DHA resulted in significant increases in the concentrations of protein in the cheesemilk (P<0·05) and cheese whey (P<0·02). The moisture-adjusted cheese yield increased significantly (P<0·01) on raising the DHA from 16 to 24 kg grass DM/cow. DHA had no significant effects on any of the gross compositional values of the cheese (although moisture and fat-in-DM levels tended to decrease and increase respectively with increasing DHA). The hardness of the uncooked cheese and functionality of cooked cheese (i.e. melt time, flowability, stretch and viscosity) were not significantly influenced by DHA over the 115 d ripening period at 4°C.

-The system of milk production in Ireland is dependent on the efficient utilisation of grazed grass. Therefore the use of grass cultivars with different heading dates may have a large effect on dairy cow performance. The objective of this study was to determine the effect of grass cultivars differing in heading date and grass ploidy on milk production and grass dry matter intake (GDMI) of spring calving dairy cows. The study took place over two years. Seventy-two spring calving dairy cows in Year 1 and 80 in Year 2 were blocked into groups of four and were assigned randomly to one of four grass cultivar treatments. The grass cultivars differed in heading date (intermediate or late) and grass ploidy (diploid or tetraploid). The grazing season began in April 12 (Year 1) and April 25 (Year 2) and lasted until the end of September in both years. A total concentrate DM input of 248 kg and 45 kg·cow -1 was offered to the herds in Year 1 and in Year 2, respectively. All concentrate was offered during the first 3 grazing rotations. Rotation had a significant effect (P < 0.001) on all milk production parameters in both years. In Year 1, late heading cultivars significantly (P < 0.05) increased milk yield, solids corrected milk yield (SCM), fat, protein and lactose yield. There was a significant interaction (P < 0.05) between heading date and grass ploidy for lactose yield and fat concentration. In Year 2, late heading cultivars had also increased milk yield (P < 0.01), lactose yield (P < 0.05), SCM (P < 0.05), protein yield (P < 0.001) and protein concentration (P < 0.05). In Year 1, the GDMI was higher (P < 0.001) for cows grazing the late heading cultivars. It is concluded that later heading grass cultivars have a beneficial effect on the milk production performance of spring calving dairy cows.dairy cows / grazing / grass cultivars / intake / milk production 321 Anim. Res. 52 (2003) Résumé -Influence de la date d'épiaison et de la ploïdie de variétés de ray-grass anglais sur les performances et l'ingestion d'herbe chez les vaches laitières au pâturage. En Irlande, les systè-mes de production laitière reposent surtout sur l'utilisation efficiente du pâturage. Dans ces conditions, la date d'épiaison des variétés de ray-grass peut avoir des conséquences sur les performances du troupeau au pâturage. L'objectif de cette étude est de déterminer l'effet de 4 variétés de ray-grass anglais, différant par leur date d'épiaison et leur ploïdie, sur la production laitière et l'ingestion d'herbe chez les vaches laitières au pâturage. Cette étude s'est déroulée durant deux saisons complètes de pâ-turage. Soixante-douze vaches en année 1 et 80 vaches en année 2, vêlant au printemps, ont été mises en lot et affectées à l'un des 4 traitements expérimentaux. Les variétés de ray-grass ont différé par leur date d'épiaison (intermédiaire ou tardif) et leur ploïdie (diploïde ou tétraploïde). La saison de pâtu-rage a commencé le 12 avril (année 1) et le 25 avril (année 2) et s'est s'achevée fin septembre. L'apport total de concent...

An experiment was carried out to determine the effect of a grass diet and a concentrate supplement on rumen fermentation and nutrient flows to the duodenum. Perennial ryegrass was cut and fed indoors to eight rumen- and duodenum-cannulated Friesian cows with or without 3 kg/d of molassed beet pulp in a randomized design experiment. The dry matter intake of grass was significantly lower for cows fed the concentrate supplement (13.6 vs. 11.5 kg of dry matter/d), but total dry matter and organic matter (OM) intakes were similar for cows fed both diets. Cows fed the supplement had higher mean concentrations of total volatile fatty acids (108 vs. 89 mmol/L) and a higher percentage of butyrate in total volatile fatty acids (13.5 vs. 11.6 mol/100 mol). There were no differences between the diets in the flow of OM to the duodenum or in the extent of OM digestion in the rumen. Flows of nonammonia N, microbial N, and amino acids to the duodenum tended to be higher for cows fed the supplemented diet than for those fed ryegrass only. The efficiency of microbial protein synthesis also tended to be higher for cows fed the supplemented diet (42 vs. 37.7 g/kg of OM apparently digested in the rumen and 28.2 vs. 26 g/kg of OM truly digested in the rumen). Overall, there were indications that the supplement caused better capture of N in the rumen and increased the efficiency of microbial protein synthesis.