Thesis (MScAgric (Animal Sciences))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The effect of Acid Buf and combinations of Acid Buf and Sodium bicarbonate in dairy cow diets on production response and rumen parameters The objective of this study was to determine the effect of Acid Buf alone, or in combination with sodium bicarbonate, on milk production, milk composition and selected rumen parameters. A high concentrate TMR, formulated to be potentially acidotic, was used to construct four dietary treatments in which Acid Buf (AB), the skeletal remains of the seaweed Lithothamnium calcareum, was used alone or in combination with sodium bicarbonate (BC). The diets contained 3.5 g/kg of AB (Treatment 1) or 1.75 g/kg of AB and 1.75 g/kg of BC (Treatment 2) or 3.5 g/kg of AB and 3.5 g/kg of BC (Treatment 3) or 3.5 g/kg of AB and 5.2 g/kg of BC (Treatment 4). The response to treatment was determined using eight ruminally cannulated lactating Holstein cows randomly allocated to treatments according to a 4 x 4 (n=2) Latin square design, with four treatments and four periods. The total experimental period was 100 days in which every cow received each diet for a period of 18 days prior to a data collection period of 7 days. Rumen pH was monitored continuously over 2 days using a portable data logging system and in-dwelling electrodes. Samples of rumen fluid were collected for volatile fatty acid (VFA) analyses. During each data collection period, milk production was recorded twice daily for 7 days, whereas milk was sampled twice daily for five consecutive days for component analysis. Cows were fed ad libitum and dry matter intake was recorded individually. Treatment had no significant effect on milk production, milk composition or feed intake. Ruminal pH profiles of all the treatments indicated that the diets were well buffered. Average pH over 24 hours was 6.0, 6.1, 6.1 and 6.2 for Treatments 1, 2, 3 and 4, respectively. The pH did not go below 5.8 for any of the treatments and increasing levels of sodium bicarbonate increased the diurnal profile such that at the highest level (Treatment 4), the pH profile ranged from 6.1 to 6.5. Although not significant, Treatment 1 (Acid Buf alone) numerically resulted in the highest milk output without compromising milk quality. It is proposed that high rumen pH may impact negatively on milk output by increasing the acetate:propionate ratio to the detriment of rumen efficiency. Treatment had no significant effect on total VFA concentration, but there seemed to be a tendency for increased total VFA concentration as the level of sodium bicarbonate increased. The acetate:propionate ratio of Treatment 1 (2.91) was significantly lower than Treatment 4 (3.65) (P<0.05). The use of buffers which react to increasing acidity in the rumen may therefore provide an efficient, safe solution to rumen acidosis. This study confirmed previous results indicating that a daily intake of 80 g of Acid Buf by cows receiving high concentrate diets would support high milk production without compromising milk solids contents. / AFRIKAANSE OPSOMMING: Die effek van Acid Buf en kombinasies van Acid Buf en Natriumbikarbonaat in melkkoeidiëte op melkproduksie, melksamestelling en rumenparameters Die doel van die studie was om die invloed van Acid Buf alleen, of in kombinasie met natriumbikarbonaat, in melkbeesdiëte op melkproduksie en melksamestelling, asook op bepaalde rumenparameters, te bepaal. ‘n Volledige dieet met ‘n hoë kragvoerinhoud, wat geformuleer is om potensieel asidoties te wees, is gebruik om vier dieetbehandelings saam te stel waarin Acid Buf (AB), die skeletoorblyfsels van die seegras Lithothamnium calcareum, alleen of in kombinasie met natriumbikarbonaat (BK) gebruik is. Een basale diet is dus geformuleer en die behandelingsdiëte het onderskeidelik 3.5 g/kg AB (Behandeling 1) of 1.75 g/kg AB en 1.75 g/kg BK (Behandeling 2) of 3.5 g/kg AB en 3.5 g/kg BK (Behandeling 3) of 3.5 g/kg AB en 5.2 g/kg BK (Behandeling 4) bevat. Agt rumen-gekannuleerde lakterende Holsteinkoeie is ewekansig aan die behandelings toegeken in ‘n 4 x 4 (n=2) Latynse vierkantontwerp met vier behandelings en vier periodes. Die totale eksperimentele periode was 100 dae, waartydens elke koei elke behandeling vir 18 dae ontvang het voor die datakolleksieperiode van 7 dae. Rumen pH is voortdurend, elke vier minute, oor ‘n twee-dae periode gemeet met behulp van draagbare dataloggers en pH elektrodes wat binne-in die rumen gesetel was. Rumenvloeistof is versamel vir die bepaling van vlugtige vetsuurkonsentrasies. Gedurende elk van die datakolleksieperiodes is die melkproduksie twee maal per dag geneem vir sewe agtereenvolgende dae en melkmonsters is tweemaal per dag versamel vir vyf agtereenvolgende dae vir komponent–analise (samestelling?). Koeie is ad libitum gevoer en voerinnames is individueel bepaal. Die behandelings het geen betekenisvolle invloed op melkproduksie, melksamestelling of voerinnames gehad nie. Rumen pH profiele van al die behandelings het aangedui dat die diëte goed gebuffer was. Die gemiddelde pH oor 24 uur was 6.0, 6.1, 6.1 en 6.2 vir Behandeling 1, 2, 3 en 4, onderskeidelik. Die pH het nie onder 5.8 gedaal vir enige van die behandelings nie en die toenemende vlakke van natriumbikarbonaat het ‘n verhoging in die daaglikse pH-profiele tot gevolg gehad. By die hoogste buffervlakke (Behandeling 4) het die pH-profiel tussen 6.1 en 6.5 gevarieer. Hoewel nie betekenisvol nie, het Behandeling 1 (slegs Acid Buf) numeries die hoogste melkproduksie getoon, sonder dat melkkwaliteit beïnvloed is. Dit is voorgestel dat te hoë rumen pH ‘n nadelige impak op melkproduksie kan hê, as gevolg van ‘n verhoogde asetaat:propionaat verhouding wat rumen doeltreffendheid benadeel. Behandelings het geen betekenisvolle invloed op totale vlugtige vetsuurkonsentrasies gehad nie, maar daar was ‘n neiging vir hoër totale vlugtige vetsuurkonsentrasies namate die vlakke van natriumbikarbonaat verhoog het. Die asetaat:propionaat verhouding van Behandeling 1 (2.91) was betekenisvol laer as dié van Behandeling 4 (3.65). Die gebruik van buffers wat reageer op toenemende suurheidsgraad kan dus aangewend word as ‘n doeltreffende en veilige oplossing vir rumen asidose. Die studie het bevestig dat ‘n daaglikse inname van 80 g Acid Buf deur koeie wat ‘n hoë kragvoerdieet ontvang, hoë melkproduksie ondersteun sonder dat melksamestelling nadelig beïnvloed word.