The objective of this study was to compare the effect of milking frequency (once vs. twice-daily milking) and breed (Holstein-Friesians vs. Jerseys) on milk and milk solids (MS; milk fat + milk protein), yield per cow, milk composition, somatic cell count and lactation length; cow body weight, body condition score, and reproductive performance over a 4-yr period. Total cow numbers in each herd were 30, 35, 36, and 42 for Holstein-Friesians milked once or twice daily, and Jerseys milked once or twice daily, respectively. Forty hectares of pasture were subdivided into 4 smaller pastures of 10 ha each. Stocking rates for the once-daily herds were 16.7% greater than the twice-daily herd in their respective breed. An increased stocking rate was chosen to achieve equal milk and MS per ha from the 2 milking frequencies. Annual milk, fat, protein, and lactose yields per cow were less for once-daily than for twice-daily milking. Interactions were detected between milking frequency and breed for annual milk, fat, protein, and lactose yields per cow, because Jerseys were relatively less affected by once-daily than by twice-daily milking than Holstein-Friesians. Holstein-Friesian cows milked once daily produced 31.2% less milk and 29.4% less MS per cow than their twice-daily counterparts. In contrast, Jersey cows milked once daily produced 22.1% less milk and 19.9% less MS per cow than their twice-daily counterparts. Milk per ha was 17.7 and 9% less for the once-daily Holstein-Friesians and once-daily Jersey herds, respectively, compared with their twice-daily counterparts, because the greater stocking rate for the once-daily herds did not fully compensate for the milk loss per cow. Milking once daily increased somatic cell count throughout the year in both breeds. Cows milked once daily conceived 3 d earlier, took 5 d less from calving to conception, and needed 11% fewer controlled internal drug release devices than those milked twice daily. Milking once daily is a viable milking option for New Zealand farmers who are prepared to trade-off loss of MS income for increased time to accomplish other non-milking activities.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The proposition that large herbivores make foraging choices which maximize intake rate was examined in two experiments on discrimination by sheep grazing pairs of swards (patches) varying in composition of two botanical components, grass and clover, and varying in sward surface height. 2. Patch selection was influenced by sward height and by clover content, and their effects were additive. Tall patches were preferred, and intermediate contents of clover were selected in preference to low or high contents. This would reinforce the patchy distribution of the grass and clover components of mixed swards. Sheep did not exploit local variation in clover content within patches. 3. There was no evidence that patch choice was influenced by differences in the intake rate obtained from the two alternatives at hand, although on average the highest intake rates were obtained on tall patches with intermediate clover contents, coincident with the pattern of preference. 4. During frequent switching between patches, components of the functional response such as bite depth, bite weight and intake rate were modified by patch composition and also by the composition of the alternate patch. This short-term carry-over effect must increase the discrimination difficulties on heterogeneous vegetation. 5. It is argued that pre-consumption cues signalling patch quality are of less use to sheep than the information gained about a patch during grazing, but that this is initially distorted by recent experience; and that information constraints on the maximization of long-term intake rate will occur during frequent switching within heterogeneous vegetation.

In February 1996, 48 Friesian and Jersey cows grazed pastures containing nominally 0, 25, 50 or 75% of dry matter (DM) as white clover with the balance mainly C4 grasses at either ad lib. (50 kg DM/cow/day) or restricted (25 kg DM/cow/day) allowances. The aim of the trial was to measure the effect of clover content on milk yield and composition, and to determine the optimum clover content for milk production. Milk yields of cows on the ad lib. allowance grazing 25% clover were 22% higher (P

Our aim was to evaluate the effects of once-daily milking on the welfare of dairy cows in a pastoral-based farming system. There are concerns that cows milked only once daily may experience discomfort associated with udder distension. We evaluated the behavior, including lying time and postures, grazing patterns, and kicking behavior in the parlor, and measures of udder firmness in cows milked once daily in 2 experiments: 1) at peak lactation, comparing cows milked once (1x) or twice-daily (2x) from the time of calving (n = 4 groups; 1x and 2x treatments); and 2) during the transition from 2x to 1x milking at mid lactation (n = 12 groups; 1x, 2x, and 2x to 1x treatments or TRANS). At peak lactation, cows milked 1x were more likely to lie with their hind legs touching the body than cows milked 2x. There were no differences in udder firmness (1x: 10.0 vs. 2x: 9.9 +/- 0.13 g of force) or kicking (1x: 25 vs. 2x: 24 +/- 7.8%) behavior in the parlor. In the second experiment, milking frequency was reduced from 2x to 1x and this change resulted in an increase in udder firmness (1 x: 9.1, 2x: 9.3, and TRANS: 9.5 +/- 0.14 g of force). Despite these differences in udder firmness, lying time (1x: 10.1, 2x: 9.5, and TRANS: 9.6 +/- 0.38 h/24 h), postures, and concentrations of fecal glucocorticoid metabolites (1x: 10.0, 2x: 10.5, and TRANS: 10.4 +/- 0.49 ng/g of feces in the 3 d after transition) in cows milked 1x or 2x were similar. Although milking frequency did not influence total time spent grazing, the diurnal grazing pattern of cows milked 2x was disrupted by afternoon milking at both peak and mid lactation. Cows milked 2x were able to compensate for this by grazing more after the return to pasture (DIM 153 to 155, 1x: 52 vs. 2x: 66 +/- 6.2 min/90 min of grazing). Cows milked 1x had slightly longer strides than 2x cows at mid lactation (1x: 0.73, 2x: 0.70, and TRANS: 0.70 +/- 0.014 strides/m). In conclusion, under our experimental conditions, we found no overt changes in behavior or physiology to indicate that the welfare of cows milked 1x is impaired.

Regulation of milk synthesis and secretion is controlled mostly through local (intramammary) mechanisms. To gain insight into the molecular pathways comprising this response, an analysis of mammary gene expression was conducted in 12 lactating cows shifted from twice daily to once daily milking. Tissues were sampled by biopsy from adjacent mammary quarters of these animals during the two milking frequencies, allowing changes in gene expression to be assessed within each animal. Using bovine-specific, oligonucleotide arrays representing 21,495 unique transcripts, a range of differentially expressed genes were found as a result of less frequent milk removal, constituting transcripts and pathways related to apoptotic signaling (NF-kappaB, JUN, ATF3, IGFBP5, TNFSF12A) mechanical stress and epithelial tight junction synthesis (CYR61, CTGF, THBS1, CLDN4, CLDN8), and downregulated milk synthesis (LALBA, B4GALT1, UGP2, CSN2, GPAM, LPL). Quantitative real-time PCR was used to assess the expression of 13 genes in the study, and all 13 of these were correlated (P < 0.05) with values derived from array analysis. It can be concluded that the physiological changes that occur in the bovine mammary gland as a result of reduced milk removal frequency likely comprise the earliest stages of the involution response and that mechano-signal transduction cascades associated with udder distension may play a role in triggering these events.