Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.674961
Title: Effects of cow genetic merit, genotype and diet forage proportion on energetic efficiency and enteric methane emissions in lactating dairy cows
Author: Dong , Lifeng
ISNI:       0000 0004 5370 3623
Awarding Body: Ulster University
Current Institution: Ulster University
Date of Award: 2015
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Abstract:
Four desktop studies were conducted to investigate the effects of animal and dietary factors on metabolisable energy (ME) requirement for maintenance (MElli)' efficiency of utilisation of ME for lactation (kl), and enteric methane (CH4) emission rates in lactating dairy cows at the Agri-Food and Biosciences Institute, Hillsborough. The data used in these studies involved nearly 1000 observations of Holstein-Friesian (HF), Norwegian and HF crossbred with Jersey or Norwegian (Fl hybrid) dairy cows, and were collated from 32 respiration calorimeter experiments between 1992 and 2010. Study 1, 3, and 4 evaluated the effect of animal factors and dietary forage proportion on energy metabolism. Study 2 focused on the examination of cow genetic merit influencing the enteric CH4 emission rates. In Study 1, 670 observations of lactating HF dairy cows with various genetic merit indexes were collated. Cow genetic merit in the United Kingdom (UK) is described using two economic indexes, Profit Index (PIN) and Profitable Lifetime Index (PLI). The PIN is based solely on milk production (n = 736, -£30 to +£63), PLI includes milk production and a number of other functional traits including health, fertility and longevity (n = 548, -£131 to +£184). The MEm for individual cows was calculated from heat production (HP) minus energy losses from inefficiencies of ME use for lactation, energy retention and pregnancy, and the kl was obtained from milk energy output (EI) adjusted to zero energy balance (EI(o») divided by ME available for production. Analysis of variance (ANOVA) and linear mixed regression technique were used to examine the effects of cow genetic merit on the MEm and the lq, As there was no significant relationship between cow genetic merit and calculated values of MEm (MJ per kg metabolic body weight, MJ/kgo.7S) or kl using the whole PIN and PLI data set, further analysis was conducted by dividing each dataset of PIN « £3, £3 to £15 and> £15) and PLI « £23, £23 to £67 and> £67) into three sub-groups categorising as low, medium and high genetic groups. Linear relationships between cow genetic merit and energetic parameters were developed to evaluate if there was any significant difference among the coefficients or constants when a common constant or coefficient was used. No significant relationship was found between ME intake (MJ/kgo.7s) and MEm (MJ/kgo.7s), EI(o) (MJ/kgo.7s) or HP (MJ/kgo. 7S) within PIN or PLI sub-groups. These results indicated that cow genetic merit may have no effects on maintenance metabolic rate or energetic efficiency for lactation and high yielding HF cows need more nutrient supply to maximise the production potential. The following study (Study 2) was conducted to investigate the effect of cow genetic merit on the enteric CH4 emissions rates using the same dataset as used in Study 1. The animals had a large range of days in milk (18 to 354), energy corrected milk yields (16.0 to 45.6 kg/d), and CH4 emissions (138 to 598 g/d). The data were analysed using the same programmes as used in Study 1 (AN OVA and regression technique) with the effects of a number of animal and diet factors removed. Within the PIN and PLI datasets there were no significant difference among the three sub-groups in terms of CH4 emission per kg feed intake, energy corrected milk yield, or CH4 energy (CH4-E) output as a proportion of energy intake (P > 0.05). Linear mixed regression using the whole PIN and PLI datasets also demonstrated that there was no significant relationship between either PIN or PLI, and CH4 emission per kg of feed intake or CH4-E output as a proportion of energy intake (P > 0.05). These results indicate that cow genetic merit has little effect on enteric CH4 emissions as a proportion of feed intake. Enteric CH4 production may mainly relate to total feed intake and dietary nutrient composition. effects of a number of animal and diet factors removed. Within the PIN and PLI datasets there were no significant difference among the three sub-groups in terms of CH4 emission per kg feed intake, energy corrected milk yield, or CH4 energy (CH4-E) output as a proportion of energy intake (P > 0.05). Linear mixed regression using the whole PIN and PLI datasets also demonstrated that there was no significant relationship between either PIN or PLI, and CH4 emission per kg of feed intake or CH4-E output as a proportion of energy intake (P > 0.05). These results indicate that cow genetic merit has little effect on enteric CH4 emissions as a proportion of feed intake. Enteric CH4 production may mainly relate to total feed intake and dietary nutrient composition.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.674961  DOI: Not available
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