A comparative study of voluntary intake and rumen digestion by deer, goats and sheep : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
The following experiments were carried out to study the voluntary feed intake and rumen digestion of Red Deer and Angora-NZ feral goats, compared to Border-Leicester/Romney cross sheep, namely: (1) Intake and utilisation of a low quality threshed prairie grass straw (13.7 g N/Kg DM) by goats and sheep; (2) chewing behaviour per 24 h during eating and ruminating by goats and sheep fed on lucerne hay, and the efficiencies of chewing during eating and ruminating upon the breakdown of feed particles; (3) seasonality in nutrient supply by deer, goats and sheep fed on a medium quality lucerne hay diet (28.3 g N/Kg DM) in summer and in winter, and (4) the role of melatonin (Me) in the control of seasonal VFI in Red Deer. 1. Goats showed a superior utilisation of the low quality forage diet, with a greater voluntary intake (g/Kg W0.75/d) of DM (55.6 g vs 33.8 g) and DDMI (17.4 g vs 8.2 g), apparent digestibilities of DM (31.2% vs 24.3%) and total fibre (36.8% vs 32.6%), especially that of lignin (11.3% vs 5.3%), when compared to sheep. The greater VFI (g/Kg W0.75/d) by goats was associated with a larger rumen pool size (g/Kg W0.75 of (DM + liquid) by goats than sheep (334.7 g vs 213.5 g). The superior fibre digestibility by goats was associated with a greater rumen NH3-N concentration (mg N/L: 115 mg vs 80 mg), greater production rates of NH3-N in the rumen (IRL: g N/Kg W0.75/d of 0.84 for goats and 0.49 for sheep). A mechanism for increasing rumen NH3-N concentration in goats was apparent through slower rates of inflow and outflow of water from the rumen (g/g DMI/d). Goats also showed greater rumen molar proportions of valerate and butyrate, and a tendency for a longer rumen MRT (h) of particulate DM (lignin and Ru-Phen), compared to sheep. Goats had smaller proportions (5.1% vs 9.6%) of large particles (>4.0 mm), and greater proportions (19.4% vs 16.1%) of small particles (<1.0 mm) in the rumen contents than sheep. The factors listed above would all favour the potential growth and attachment to feed particles of fibre-digesting bacteria in the rumen of goats, compared to sheep. 2. Goats spent more time chewing during eating (+3.1 h/24 h) and less time chewing during ruminating (-2.2 h/24 h) than sheep when fed on lucerne hay. Goats had a greater number of chews/min spent eating (154 vs 128) than sheep, and a smaller number of chews during ruminating (79 vs 100) than sheep. The efficiency of chewing during eating in breaking down feed particles to <1.0 mm (<C.EAT>) was greater by goats than by sheep (85% vs 48%) and <C.RUM> was smaller by goats than sheep (48% vs 59%). When corrected for the number of chews spent chewing during eating and ruminating, the differences in <C.EAT> and <C.RUM> between goats and sheep disappeared (for <C.EAT>, 2.1% vs 2.4%; for <C.RUM>, 0.6% vs 0.6%). 3. Sheep showed no evidence of seasonal cycles of VFI when fed on lucerne hay. In contrast to sheep, deer showed marked seasonal cycles of an increase in summer of voluntary DMI (+33.8%), DDMI (+29.9%), MEI (+25%), apparent fibre digestibility (+11.2%), MRT of lignin (+26%), rumen pool of DM + liquid (51.3%), internal recycling of water to the rumen (+74.1%), rumen NH3-N concentration (+56.4%) and Ac/Pr ratio (+16%). All the cycles showed a trough in winter and a marked increase in summer. The expansion in the rumen pool size, a longer rumen MRT of digesta and a greater recycling of water into the rumen, allowed for an increase in VFI (without depressing apparent DMD), and for an increase in apparent fibre digestibility in summer. Goats also showed an increase in voluntary DMI in summer (+19.7%), associated with increases in a number of rumen digestive functions, which were all not as marked as for deer. Unlike deer, the increased VFI in summer occurred at the expense of a reduced apparent DMD (-9.8%) and fibre digestibility (-5.8%). Deer showed a faster rumen FOR of liquid (15.6%/h) than goats (10.0%/h) and sheep (10.4%/h) both in summer and in winter. Goats digested lignin, the least digestible component of fibre, more efficiently than sheep, both in summer (18.9% vs 14.6%) and in winter (21.9% vs 9.4%). The greater fibre digestibility by goats than sheep in winter was associated with a greater rate of NH3-N production in the rumen (IRL of 1.13 g vs 0.98 g (g N/Kg W0.75/d)). The threshold to passage of particles through the reticulo-omasal orifice was 1.0 mm for deer, goats and sheep, with more than 98% of the particles in the faeces being <1.0 mm. 4. Exogenous subcutaneous implants of melatonin (Me) in spring in castrated male Red Deer caused reductions in VFI, water-filled rumen capacity, rumen digesta load, and heart rate (beats/min), to occur in both early and in late summer. Melatonin possibly entrains the seasonal cycles of VFI in Red Deer to photoperiod, and controls the seasonality of VFI. Methods are suggested for reducing the magnitude of the winter depression in VFI in Red Deer stags, using immunisation against Me.