@conference {3672,
	title = {Estimation of genetic parameters for milk yield traits at different herd production levels in cows milked once- or twice-daily in New Zealand},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {76},
	year = {2016},
	month = {07/2016},
	pages = {49-53},
	address = {Adelaide},
	abstract = {The objective of this study was to estimate genetic parameters for lactation yields of milk (MY), fat (FY) and protein (PY) for cows
milked either once- (OAD) or twice-a-day (TAD) at different production levels (PL), calculated as average milk solids yield (FY
+ PY) for dairy cattle in New Zealand. Lactation records of 124,620 and 194,631 cows from 298 and 350 herds milked OAD and
TAD, respectively were used. Heritiabilities (h2) were lower in low PL herds milked OAD compared to low PL herds milked TAD
(0.11-0.18 vs. 0.22-0.37). Across PL, h2 for MY at medium and high PL were greater than 0.30 at both MF, while for FY and PY,
those values were less than 0.30. Genetic correlations (rG) between MY and PY were greater (>0.70) compared to rG between FY
and any of the other traits (<0.65). The lowest rG was observed between MY and FY at low PL (0.09{\textpm}0.087). In conclusion, lower
h2 at low PL from cows milked OAD reveal unequal genetic expression of milk traits genes compared to higher PL. Ignoring the
heterogeneity of variance in the genetic evaluation could result in systematic inaccuracies and biases in the estimation of breeding
values for cows milked OAD.},
	issn = {1176-5283},
	author = {Lembeye F and Lopez-Villalobos N and Burke JL and Davis SR}
}
@conference {3672,
	title = {Estimation of breed and heterosis effects for milk traits and somatic cell scores in cows milked once and twice daily in New Zealand},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {75},
	year = {2015},
	month = {07/2015},
	pages = {60-63},
	address = {Dunedin},
	abstract = { Crossbreeding is widely used by famers milking twice-a-day (TAD) to increase farm profitability. Effects of crossbreeding on farm
productivity and profitability have not been investigated in farms practicing once-a-day (OAD) milking. The aim of the study was
to estimate breed and heterosis effects for lactation length (LL), total yields of milk (MY), fat (FY) and protein (PY) and average
somatic cell score (SCS) in cows milked OAD or TAD. Records from 36,276 Friesian (F), 31,560 Jersey (J) and 90,081 crossbred
(F{\texttimes}J) cows that calved in spring between 2008 and 2012 were used. Compared to J cows, F cows had a higher MY (657 kg in
OAD and 1034 kg in TAD), FY (2.9 kg in OAD and 7.8 kg in TAD), PY (13.6 kg in OAD and 22.4 kg in TAD) and SCS (0.28
in OAD and 0.05 TAD). Lactation length in OAD cows was five days shorter than in TAD cows (P<0.05). These results show
a significant interaction between breed and milking frequency for production traits (P<0.001). Expressed as a percentage of the
average of parental breeds, first-cross heterosis effects ranged between 4.92 to 6.84\% for production traits, and were similar across
milking frequencies. The estimates of breed and heterosis obtained in this study can be used for simulation studies to evaluate the
profitability of crossbreeding systems under OAD and TAD milking systems of typical New Zealand dairy farms.},
	issn = {1176-5283},
	author = {Lembeye F and Lopez-Villalobos N and Burke JL and Davis SR}
}
