The role of Calcareous Marine Algae in Reducing the Negative Health and Production Consequences of Disrupted Rumen Fermentation in Dairy Cows

The objective of the thesis was to investigate the effects of calcareous marine algae (CMA) on rumen pH and fermentation, digestion, feed intake, milk production, and inflammation in dairy cows during a dietary challenge. Different types of dietary challenges were used to achieve our objective. The dietary challenges included: the transition period; a high starch total mixed ration (TMR), a grain (GR) induced sub-acute ruminal acidosis (SARA); and a ryegrass (RY) induced SARA. Calcareous marine algae was compared to a control (CON) diet, containing no dietary additive, in chapter 3, 5, and 6. In chapter 4, CMA was compared to a combination of CMA and marine magnesium oxide (MM), sodium bicarbonate (SB) and a CON treatment. Chapter 3 investigated the effects of CMA on feed intake, milk production, energy balance, serum mineral metabolites and inflammatory markers in 32 cows during the transition period compared to a CON treatment. The CMA treatment had higher prepartum dry matter intake (DMI), postpartum DMI, milk fat concentration, fat corrected milk yield, and reduced plasma serum amyloid A (SAA) compared to the CON treatment. Chapter 4 investigated the effects of CMA, with or without MM, and SB on rumen pH parameters, volatile fatty acid (VFA) production, apparent total tract digestion, and the kinetics of digestion using 4 cannulated cows in a 4 × 4 Latin square design. The CMA and CMA+MM increased mean, median and minimum rumen pH, and reduced time spent below rumen pH 5.6 and 5.4 compared to the CON treatment. There was less variation in rumen pH with the CMA treatment compared to the SB treatment. Acetate: propionate ratio was reduced, and the molar proportion of propionate increased with CMA+MM compared to CON, CMA, and SB. The CMA+MM treatment increased neutral detergent fibre (NDF) digestibility compared to CON. There were no differences in rumen fluid and particulate outflow rates, rumen retention time, or rumen in-sacco degradability between treatments. Chapter 5 determined the effects of CMA on rumen pH, rumen fermentation, and plasma inflammatory markers during a GR and RY induced SARA challenge using eight ruminally cannulated cows in a 2 × 2 split-plot crossover design. The experiment consisted of three phases: acclimatisation; challenge; and recovery. Both GR and RY diets successfully induced SARA temporarily. The CMA treatment reduced the minutes below rumen pH 5.4, 5.6, and 5.8 during the ACC phase, and minutes below rumen pH 5.6 and 5.8 during the REC phase. The RY diet had a lower concentration of rumen lipopolysaccharide compared to the GR diet during the challenge. There was a greater reduction in SAA with the CMA treatment compared to the CON during the recovery phase. Chapter 6 investigated the effects of CMA on feeding behaviour, rumen fermentation products, milk fatty acid profiles, and total tract digestibility of dry matter (DM) and organic matter (OM) in 32 early lactation dairy cows compared to a CON treatment. The CMA treatment reduced the proportion of trans-9 18:1 fatty acid and the omega-6 to omega-3 fatty acid ratio in milk compared to the CON treatment. Daily TMR intake and feeding rate were increased in cows fed the CMA treatment compared to cows fed the CON treatment. These findings demonstrate the benefits of CMA on reducing rumen pH depressions and increasing digestion of DM and OM. Calcareous marine algae can be an effective tool for preventing rumen fermentation disruptions during a dietary change and for increasing DMI and energy balance during the transition period.