SPECIAL REPORT | FODDER BEET
Acidosis hazard with lactating cows
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Words by: Anne Lee
incoln University PhD student Anita Fleming is warning more work needs to be done on how to safely feed fodder beet to lactating dairy cows and is suggesting farmers may have to feed smaller amounts more frequently to avoid animal health problems. The recommendation stems from her three-year PhD study that included experiments with lactating cows in spring on the university’s research dairy farm. Her PhD, which also included modelling, looked in detail at the effect on the rumen, the impact on the animal and the herd and analysed the farm system in terms of profit and risk. She’s concerned that despite using best practice transitioning methods two of the eight cows (25%) used in her onfarm experiment developed sub-acute ruminal acidosis (SARA), even at small levels of fodder beet feeding. Her findings mirror those of DairyNZ’s Garry Waghorn and AgResearch’s David Pacheco. The experiment was published in the scientific journal Animals earlier this year. Despite the small number of animals involved Anita says the experimental design was robust enough to back up her assertion that 25% of cows in a herd could be at risk of SARA. “We found that despite using the recommended ‘gold standard of transition’ – increasing the amount of fodder beet fed each day by 0.5kg drymatter (DM)/ cow/day, feeding them after morning milking and leaving them for up to two hours to ensure they had fully eaten their individual allocation, 25% of the animals still developed SARA. The cows were fed individually on harvested fodder beet
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PhD student Anita Fleming and her research supervisor Professor Pablo Gregorini.
with the leaf removed and were held at the covered yard area until they had eaten their allocations. SARA is characterised by the accumulation of volatile fatty acids (VFA) which reduce rumen pH. A pH less than 5.8 for more than three hours is defined as marginal SARA while a pH of less than 5.6 for more than three hours is defined as severe SARA. In Anita’s study four cows were fed fodder beet while the other four were fed on pasture only for 20 days with rumen, blood and milk sampling carried out over the period. They then had a five-day “washout” period and the animals were swapped over and the experiment carried out again with cows that had been fed pasture transitioned on to fodder beet and those that had been fed fodder beet plus pasture in the first period fed pasture only. The pasture-only cows were fed 19kg DM/day high quality ryegrass and white clover pasture allocated to each animal in an individual strip while the fodder beet cows were offered pasture in the same way and at the same pasture allocation but were supplemented with up to 6kg DM/cow/ day of fodder beet, with that upper limit
reached following a transitioning process. Anita found that one cow in the first period developed SARA on day 10 of adaptation to the fodder beet with her pH dropping below 5.5 for four hours. Her allocation was reduced to 3kg DM/day and she was maintained at that until the end of the first period of the experiment. Another cow also developed SARA towards the end of the transition period with a pH of less than 5.5 for between 110 minutes and 190 minutes per day. Her allocation was also reduced but neither cow was removed from the study because pH stabilised without intervention, which is a defining characteristic of SARA. Anita collected milk samples, blood samples, rumen content samples and measured rumen pH every 10 minutes using a wireless bolus in the rumen. She analysed amino acids and non-esterified fatty acid (NEFA) in blood, milk urea nitrogen (MUN), milk yield, fat, protein and lactose and milk fatty acid profiles, rumen pH, VFA, ammonia and L-lactate in rumen samples. She also analysed both the fodder beet and pasture quality information including
Dairy Exporter | www.nzfarmlife.co.nz | November 2020
