Diets offered to grazing dairy cows can vary considerably in their dietary cation-anion difference (DCAD) and are often well in excess of what has been considered optimal. The effects of a range of DCAD on the health and production of pasture-based dairy cows in early lactation was examined in a randomized block design. Four groups of 8 cows were offered a generous allowance of pasture (45 +/- 6 kg/d of dry matter (DM) per cow) for 35 d and achieved mean pasture intakes of approximately 17 kg/d of DM per cow. Cows were drenched twice daily with varying combinations of mineral compounds to alter the DCAD. Dietary cation-anion difference ranged from +23 to +88 mEq/100 g of DM. A linear increase in blood pH and HCO(3)(-) concentration and blood base excess, and a curvilinear increase in the pH of urine with increasing DCAD indicated a nonrespiratory effect of DCAD on metabolic acid-base balance. Plasma concentrations of Mg, K, and Cl declined as DCAD increased, whereas Na concentration increased. Urinary excretion of Ca decreased linearly as DCAD increased, although the data suggest that the decline may be curvilinear. These results in conjunction with the increased concentrations of ionized Ca suggest that intestinal absorption of Ca or bone resorption, or both, increased as DCAD declined. Dry matter intake, as measured using indigestible markers, was not significantly affected by DCAD. However, the linear increase in the yield of linolenic acid, vaccenic acid, and cis-9, trans-11 conjugated linoleic acid in milk, as DCAD increased is consistent with a positive effect of DCAD on DM intake. Increasing DCAD did not significantly affect milk yield or milk protein, but the concentration and yield of milk fat linearly increased with increasing DCAD. The increased milk fat yield was predominantly a result of increased de novo synthesis in the mammary epithelial cells, although an increase in the yield of preformed fatty acids also occurred. Milk production results suggest that DCAD for optimal production on pasture diets may be higher than the +20 mEq/100 g of DM previously identified for total mixed rations.

The objective of this study was to investigate the effects of contrasting nutritional regimens on milk composition from cows of different protein phenotypes. Twenty sets of seasonally calving identical twin cows that constituted five different protein phenotypes (four sets of twins per phenotype) were subjected to two nutritional treatments in crossover experiments during spring (early lactation) and summer (mid to late lactation). The phenotypes studied allowed a comparison of the AA, AB, and BB variants of both beta-lactoglobulin (beta-LG) and kappa-casein. Nutritional treatments were 1) ad libitum grazing (i.e., cows were allocated a pasture allowance of approximately 40 kg of dry matter/d per cow) plus 5 kg of a concentrate based on barley and 2) restricted grazing (pasture allowance of 20 kg of dry matter/d per cow). Milk samples were collected from each cow near the end of each 14-d treatment period and were analyzed for a detailed range of individual protein and fat constituents. Diet had significant effects on the concentrations of all milk components measured. Protein phenotype affected some protein components but not fat components. Interactions between the effects of beta-LG phenotype and diet were noted for the concentrations of some milk components. Diet and protein phenotype have important effects on the manufacturing potential of milk produced under the dairying systems of New Zealand, which rely heavily on grazing. The effects of nutrition on milk composition may depend on the beta-LG phenotype.

Sources of variation in milk protein composition were determined after approximately 203 days-in-milk for spring-calving Friesian cows grazing ryegrass-white clover pastures in New Zealand. Three groups each of 15 multiparous cows were managed as separate herds. Each herd was subjected to one of three management strategies: pasture only, pasture supplemented with 2-3 kg cow 1 d -1 maize grain, and pasture plus 5-6 kg cow -1 d -1 maize grain and 3-4 kg cow -1 d -1 pasture silage. During a 3-week period beginning in February 1994, milk samples were collected twiceweekly from individual cows and the detailed protein composition determined. Variation was observed in milk yield and the concentrations of all protein components measured, with betweencow variation being greater than within-cow variation for all parameters except non-protein N and urea. Supplementing pasture with maize grain and/or silage increased milk yield but had only minor effects on protein composition. These data will enable increased efficiency of experimental design in this research area, and provide details of the natural variation in milk protein composition. This variation gives an indication of the extent that *Author for correspondence A98046 Received 9 September 1998; accepted 7 April 1999 milk protein composition could be manipulated by on-farm practices, or through the selection of cows with defined milk protein profiles.

Sources of variation in milkfat characteristics were determined after approximately 115 days-in-milk for Friesian cows that had calved in spring and grazed ryegrass-white clover pastures.

Devices used by automated milking systems are similarly accurate in estimting milk yield and in collecting a representative milk sample compared with devices used by farms with conventional milk recording Kamphuis, C.; Bela Rue, B.; Turner, S.-A.; Petch, S.-F This is a "Post-Print" accepted manuscript, which has been published in the "Journal of Dairy Science"This version is distributed under a non-commencial no derivatives Creative Commons (CC-BY-NC-ND) user license, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited and not used for commercial purposes. Further, the restriction applies that if you remix, transform, or build upon the material, you may not distribute the modified material.Please cite this publication as follows: In New Zealand, milk recording standards were developed before AMS technology 77 was an option. Therefore, the standards only allow submission of milk recording data into the MATERIALS AND METHODS 103Data used for this study originated from two separate but parallel running studies and, 104 therefore, will be described in two separate sections. 206Before the current study commenced, certified providers were requested to install the 207 milk sampling devices as used in the field without any special preparations. One certified 208 provider, however, did calibrate these devices specifically for this study.