Browsing by Author "Van Dyk, Nelita"

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    Buffer supplementation in concentrates for Jersey cows grazing spring ryegrass pasture
    (Stellenbosch : Stellenbosch University, 2015-03) Van Dyk, Nelita; Cruywagen, C. W.; Meeske, R.; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Pasture is the cheapest available source of nutrients and in the Southern part of the Western Cape of South Africa the most common used pasture system is kikuyu grass, over-sown with ryegrass. For this reason, it is important to optimally utilise the pasture and to ever try to improve pasture based feeding systems. High quality ryegrass creates a risk for subclinical rumen acidosis (SARA) for dairy cows. Supplementing concentrates, which is inevitable as energy is the first limiting nutrient for dairy cows, increases the risk of incidence. The addition of buffers to total mixed ration feeding systems has achieved great success in diets containing high levels of concentrates. Information on buffers regarding pasture based systems is, however, lacking, especially pertaining to SARA. The cost of adding buffers to concentrates fed to grazing dairy cows is a concern. If, however, there is a challenge on the rumen, buffer addition has proved to increase the milk fat content and therefore the increased income might justify the expense. The purpose of this study was to determine whether the addition of buffers to concentrates supplemented to grazing dairy cows could utilise pasture optimally, whilst increasing milk yield and improving milk composition, and maintaining rumen functioning. Fifty four high producing Jersey cows were blocked according to milk yield, days in milk and lactation number. Cows within blocks were then randomly allocated to one of three treatments. Treatments included no buffer inclusion (CON), Acid Buf (AB) at a level of 10 g/kg and sodium bicarbonate (SB) at a level of 20 g/kg of the concentrate DM. Cows received 6.6 kg “as is” concentrate per day, consisting of 62% maize, 15% hominy chop, 11% bran, 4% soybean oilcake, 4% molasses, minerals and vitamins. Buffers were mixed into the concentrates beforehand to ensure intakes of 120 g of sodium bicarbonate or 60 g of Acid Buf per cow/day. Cows grazed high quality ryegrass during spring and were allocated 10 kg DM pasture per cow/day with ad libitum access to fresh water. Milk production was recorded daily and milk composition fortnightly, after an adaptation period of 14 days. Six ruminally cannulated Jersey cows grazed with the production study cows, to be used for a separate rumen study. These cows were divided into three groups of two and were allocated to each treatment. Cows were crossed-over through-out the duration of the trial to ensure that all cannulated cows received each treatment. An in sacco digestibility trial was done and rumen pH and volatile fatty acid (VFA) concentrations were also determined. Milk production (kg/day) was 20.2, 20.3 and 20.5, whereas 4% fat corrected milk production (kg/day) was 20.8d, 21.8cd, 21.9c for the CON, SB and AB treatments, respectively. Milk fat content did not differ among treatments and was 42.4, 45.0 and 45.1 g/kg, whereas milk protein tended to be different at 34.1d, 35.6c and 35.1cd g/kg for CON, SB and AB, respectively. Milk lactose differed among treatments and was 44.9b, 47.6a and 47.6a g/kg, whereas milk urea nitrogen was 10.5a, 9.7ab, 9.6b for CON, SB and AB, respectively. Total VFA and proportions of individual VFA’s did not differ among treatments. Treatment also had no effect on mean ruminal pH and time spent below critical pH values. Pasture DM and NDF digestibility did not differ among treatments. The results indicated that milk production and rumen functioning can be maintained with the addition of buffers to grazing cows, even though no differences were found between control and buffered treatments. The milk composition was, however, favourably affected by buffers and it could be economically viable for farmers using similar production systems.