Buffer supplementation in concentrates for Jersey cows grazing spring ryegrass pasture

Van Dyk, Nelita (2015-03)

Thesis (MScAgric)--Stellenbosch University, 2015.

Thesis

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.

AFRIKAANSE OPSOMMING: Weiding is die goedkoopste voedingsbron vir melkbeeste en in die Suidelike deel van die Wes-Kaap waar kikoejoe gewoonlik oorgesaai word met raaigras, word daar altyd gepoog om beter benutting van weiding te bewerkstellig. Hoë kwaliteit weiding kan egter ‘n risiko vir subkliniese rumenasidose (SARA) inhou. Die byvoeding van kragvoere is onvermydelik, siende dat energie die eerste beperkende nutrient vir melkbeeste is en dit verhoog die risiko nog verder. Totaal gemengde rantsoene het al groot sukses behaal met die invoeging van buffers. Inligting aangaande die gebruik van buffers vir weidende melkbeeste is egter beperk, veral met betrekking tot die voorkoms van SARA. Die ekstra koste vir buffers kan ‘n rede tot kommer wees. Die insluiting van buffers is egter al bewys om die impak op die rumen te verlaag en hoër melkvet tot gevolg te hê en daarom mag die verhoogde inkomste moontlik die koste rondom buffers regverdig. Die doel van die studie was om te bepaal of bufferinsluiting in kragvoere vir weidende diere die weidingsbenutting sodanig kan optimaliseer dat melkproduksie en melk samestelling verbeter en goeie rumengesondheid terselfdertyd gehandhaaf kan word. Vier en vyftig hoë produserende Jerseykoeie is volgens melkproduksie, dae in melk en laktasienommer geblok. Koeie is vervolgens ewekansig aan een van drie behandelings toegeken. Behandelings het die volgende ingesluit: geen buffers (KON), Acid Buf (AB) teen 10 g/kg DM en natriumbikarbonaat (SB) teen 20 g/kg kragvoer. Elke koei het 6.6 kg (natuurlike vogbasis) konsentraat per dag ontvang, waarvan die samestelling as volg was: 62 % mielies, 15 % hominy chop, 11 % semels, 4 % soja-oliekoek, 4 % melasse, minerale en vitamiene. Die buffers is sodanig in die onderskeie kragvoere ingemeng om te verseker dat koeie 120 g koeksoda of 60 g Acid Buf per dag inneem. Koeie is van 10 kg DM hoë-gehalte weiding per koei/dag voorsien en koeie het vrye toegang tot skoon drinkwater gehad. Melkproduksie is daagliks aangeteken en melkmonsters is twee- weekliks geneem om melksamestelling te bepaal. Ses rumen-gekannuleerde Jerseykoeie het saam met die res gewei. Hierdie koeie is in ‘n aparte rumenstudie gebruik. Die koeie is verdeel in drie groepe van twee en deur die loop van die studie is koeie oorgeplaas op ander behandelings soadat elke koei elke behandeling ontvang het. ‘n In sacco-verteringstudie is gedoen en rumenparameters wat bepaal is, sluit in die bepaling van rumen pH en vlugtige vetsuur (VVS) konsentrasies. Melkproduksie (kg/dag) was 20.2, 20.3 en 20.5, terwyl die 4% vet-gekorrigeerde melkproduksie (kg/dag) 20.8d, 21.8cd en 21.9c kg/dag was vir die KON, SB en AB behandelings, onderskeidelik. Melkvetinhoud het nie tussen behandelings verskil nie en was 42.4, 45.0 en 45.1 g/kg, terwyl die melkproteïeninhoud, waarvan die waardes 34.1d, 35.6c en 35.1cd was vir die KON, SB en AB behandelings, onderskeidelik, geneig het om te verskil. Die laktose-inhoud het verskil tussen behandelings en was 44.9b, 47.6a en 47.6a g/kg, terwyl en melk-ureumstikstof 10.5a, 9.7ab, 9.6b was vir KON, SB en AB, onderskeidelik. Totale vlugtige vetsure (VVS) en proporsies van individuele VVS het nie tussen behandelings verskil nie. Behandeling het ook geen invloed op gemiddelde rumen pH of tyd wat pH onder kritiese waardes was, gehad nie. Weidingverteerbaarheid (DM en NDF) het nie verskil tussen die drie behandelings nie. Hierdie resultate dui daarop dat melkproduksie en rumengesondheid onderhou kan word deur die insluiting van buffers in die kragvoer vir weidende koeie, al is geen verskil tussen die kontrole en gebufferde behandelings gevind nie. Die melksamestelling is egter gunstig deur buffers beïnvloed en buffers kan ekonomies geregverdig word vir boere wat soortgelyke produksie stelsels toepas.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96712
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