The relationship between various animal and management factors and milk urea, and its association with reproductive performance of dairy cows grazing pasture

This study was designed to determine the use of milk urea to diagnose nutrient imbalances in diets of dairy cattle grazing pasture and infertility problems associated with excess dietary nitrogen (N). A first experiment investigated the influence of the ratio of N/water soluble carbohydrate (WSC) (g/g) and N/metabolisable energy (ME) (g/MJ) (% of estimated intake) in the diet, and animal and management factors, on urea concentrations of individual cow or bulk milk samples collected at monthly intervals over a 2-year period from a herd of 108 Friesian dairy cows grazing pasture. Mean+/-S.E. daily milk yield was 18.4+/-0.11 1 milk/cow with 40.3+/-0.25 mg urea/dl of milk. This relatively high milk urea value is in line with the high estimated N/WSC ratio, which was three times the recommended ratio for that level of production. The ratio of N/WSC in the diet alone explained 8.8% of the: variation in milk urea from individual cows, and this was increased to 21.5% when genetic merit, cow age, milk yield and milli protein content were included in the model. Level of feeding and cow live-weight had no significant effect on milk urea. Milk urea levels were lowest (at 32 mg/dl) when cows were between 40 and 60 days in lactation. Cows had higher (P < 0.001) levels of urea in their milk from January to June, when they grazed kikuyu grass pasture, than for the rest of the year when they grazed ryegrass pasture (43 vs. 35 mg/dl). Then was a stronger relationship between N/WSC and the urea content of bulk milk (r(2) = 30%) than individual cow milli (r(2) = 11%), and this relationship was curvilinear. Substituting ME for WSC explained a further 2% and 2.7% of variation in bulk and individual milk urea, respectively. in a second experiment, the relationship between milk urea and the rates of non-return to service of Friesian cows grazing pasture was investigated. Milk samples were collected from 556 cows on four farms on the day of artificial insemination. The urea content of milk was not related (P < 0.05) to the chances of not returning to service. From the results of this study, it may be concluded that the urea content of bulk, but not individual cow, milk is a useful tool for assessing the appropriateness of the N/WSC ratio in the diet of dairy cows grazing pasture. There was no evidence that high milk urea levels are associated with poor reproductive performance in dairy cows grazing pasture. (C) 1999 Elsevier Science B.V. All rights reserved

Effect of time of feeding carbohydrate supplements and pasture on production of dairy cows

The productivity and rumen status of Friesian cows grazing short rotation Italian ryegrass (Lolium multiflorum) pastures was examined in relation to the time of grazing and of feeding cereal-based concentrates. In experiment 1, 42 cows grazed as seven separate groups of six cows on ryegrass pasture over a 2-day period, and were fed 2 kg crushed barley grain/cow at morning and evening milking on the first day. On the second day, no concentrates were fed at morning milking and a different group of cows was removed at random from grazing and a rumen sample collected by stomach tube at 0, 1, 2, 3, 4, 5, 7 and 9 h after commencement of grazing at 07:00 h. Sampling concluded before afternoon milking at 17:00 h. Rumen ammonia (NH3) concentration peaked and pH fell to its lowest value between 7 and 9 h after cows commenced grazing. In experiment 2, 42 cows were stratified into three groups of 14 cows on the basis of milk and component yield, age, liveweight and calving date and randomly allocated within blocks to one of three treatments. Over a 10-day adjustment period and a 21-day experimental period, cows were given their daily pasture allocation of 13.5 kg DM/cow (above 5 cm stubble height) either after morning milking, and fed crushed barley grain at morning and evening milking in the ratio of 3:1 kg/cow (Synch) or 1:3 kg (Asynch) or given their daily allocation of pasture after afternoon milking with barley fed at a ratio of 3:1 kg/cow (PM) in the morning and evening milking. Based on the results of experiment 1, the feeding schedule for the Synch group was predicted to more closely synchronise the availability of N from pasture and readily fermentable carbohydrates (RFC) from concentrates, in the rumen, compared to the Asynch cows. The comparison between Synch and PM groups was to determine the relative importance of 'synchrony' compared to feeding pasture (afternoon) high in water soluble carbohydrates (WSC) content. The WSC content of ryegrass pasture sampled after morning milking (when the Asynch and Synch groups received their new pasture allocation) was 70 and 74 g/kg DM, respectively, compared to 124 g/kg DM for samples taken after afternoon milking (when the PM group received a new pasture allocation). Pasture dry matter intake (DMI) and in vivo digestibility of individual cows was determined by use of alkanes as inert markers, whilst group DMI was determined from pre- and post- grazing pasture mass estimated by rising plate meter. Rumen samples were taken by stomach tube at 0, 3, 7 and 11 h after grazing commenced in the morning on the last day of the experiment. On this same day the % of cows grazing was recorded at 10-min intervals. Nitrogen intake (733 g N/cow/day) was 280% above requirements and this resulted in rumen NH3 concentrations being three times higher than the concentration at which microbial protein synthesis (MPS) would be expected to become limited. Milk (25.1, 24.3 and 26.8 l/cow/day; (P=0.05)) and protein (809, 794 and 850 g/cow/day; P0.05) but DM digestibility was (

Rice increases productivity compared to other carbohydrate supplements in dairy cows grazing kikuyu (Pennisetum clandestinum), but not ryegrass (Lolium multiflorum), pastures

The effect of four carbohydrate supplements on the productivity of dairy cows grazing short rotation ryegrass (Lolium multiflorum) or kikuyu (Pennisetum clandestinum) pastures were assessed. When grazing kikuyu, four groups of 20 cows (14 in early and 6 in late lactation) were matched for production and live-weight and were supplemented with 4 kg dry matter (DM)/cow day of either finely rolled barley (B), finely rolled barley sucrose mix (ratio 3:1) (BS), cracked maize (M) or finely milled rice (R), over a 35-day experimental period following a 21-day adjustment period. The production of cows in early (