@conference {3672,
	title = {Calf and heifer development and the onset of puberty in dairy cows with divergent genetic merit for fertility},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {77},
	year = {2017},
	month = {06/2017},
	pages = {205-210},
	address = {Rotorua},
	abstract = {A research herd with divergent genetic merit for fertility was established to better understand the underlying drivers of fertility in dairy cattle. This paper describes the establishment of this herd, heifer growth and development, and the effect of divergence in fertility breeding value (FBV) on the timing of puberty. The average FBV of the high and low fertility groups of heifers was +5.6 and -4.6, respectively. The heifers were weighed fortnightly, with body condition score (BCS) and stature recorded at six, nine, 12 and 15 months of age. Weight and age at puberty were defined as the first day when plasma progesterone was >1 ng/ml in two of three consecutive once weekly samples. There was no effect of FBV on live weight (LWT), BCS, nor stature by age as the heifers matured. High-fertility heifers attained puberty at a lighter LWT (271 vs. 296 kg; SED 4.3 kg), an earlier age (358 vs. 379 days; SED 6.0 days) and a lower proportion of estimated mature LWT (51 vs. 55\%; SED 0.7\%), compared with Low-fertility heifers. Therefore, the premise that high genetic merit for fertility is positively associated with reaching puberty earlier is supported. Further work is required to support and assess the value of incorporating a puberty trait into the FBV.},
	issn = {1176-5283},
	author = {Meier S and Fisher B and Eketone K and McNaughton LR and Amer PR and Beatson P and Bryant JR and Dodds KG and Spelman R and Roche JR and Burke CR}
}
@conference {75864,
	title = {Economic evaluation of management strategies for a model Waikato farm to achieve a herd average body condition score of 5.0 at calving},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {71},
	year = {2011},
	month = {Jan},
	pages = {17-22},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Invercargill},
	abstract = {Industry advisers advocate a herd average body condition score (BCS) of 5 at calving to optimise profitability and system sustainability. However, the full value and cost of achieving the industry target has not been evaluated. Using the Farmax Dairy Pro model, the value of increasing the herd average BCS at calving from 4.0 to 5.0 was evaluated. A representative Waikato farm with a single dry off date in mid-May, with a herd average BCS of 4.0 at calving was modelled as the Base scenario. The profitability of seven alternative scenarios that achieved average herd BCS of 5.0 at calving were examined. Strategies that traded off autumn production to attain target BCS maintained a similar operating profit (OP) of -$46/ha to $3/ha, relative to the Base scenario. Partial season once-a-day milking increased OP by $220/ha to $269/ha, as long lactations and BCS targets were able to be achieved while reducing operating expenses. Additional supplements fed to dry cows to achieve target BCS increased OP by $43/ha. Additional mid-late lactation feeding increased OP by $139/ha to $269/ha, but only effected BCS by 0.15 units during lactation. These simulations indicate there is value in achieving recommended BCS targets, with multiple profitable strategies to do so.},
	issn = {1176-5283},
	author = {Douglas RJ and Bryant JR and Hedley P and Smeaton DC and Brazendale R and Roche JR}
}
@conference {69477,
	title = {Simulated impacts of increased nitrogen retention in dairy cows on nitrate leaching from grazed pasture},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {70},
	year = {2010},
	month = {Jun},
	pages = {86-87},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Palmerston North},
	abstract = {The intensification of grazing land has increased the amount of nitrogen (N) entering waterways, reducing their quality and clarity. Between 60 and 90\% of the N ingested by grazing cattle is excreted in urine and dung (Haynes \& Williams, 1993), providing the major source of nitrate leached from grazed pasture. Reducing the N content of urine can therefore have a major impact on nitrate leaching, which can be achieved by reducing dietary N or improving N partitioning in the animal. Some  techniques that improve N partitioning have been evaluated. These include dietary manipulation and the use of metabolism modifiers (Di \& Cameron, 2000).},
	issn = {1176-5283},
	author = {de Castro J and Bryant JR and Burggraaf VT}
}
@conference {41729,
	title = {Choice of the most appropriate models and estimation procedures of lactation curves for grazing dairy cattle},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {67},
	year = {2007},
	month = {Jan},
	pages = {209-214},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Wanaka},
	abstract = {The objective of this study was to determine the most appropriate lactation curve representation, a 4th order Legendre polynomial (LP) function or a mechanistic mammary gland (MG) model, for various lactation curve shapes of grazing cattle in New  Zealand. The ability of two optimisation methods, evolutionary algorithm (EA) and the Newton method, used to find parameter values that minimised mean prediction error (MPE) was also determined. The 95\% confidence intervals for the parameters values and goodness of fitness for each lactation function and numerical algorithm were obtained with a bootstrapping strategy. Milk yields of three different cows were chosen to describe bi-peak, highly variable, and springpeak lactation curves. The MG function was able to find the best fit between predicted and actual values for the bi-peak and highly variable lactation curves withMPE of 2.7 to 3.7\%, compared with MPE of 6.5 to 11.9\% for the LP function applying Newton and EA. For the traditional lactation curve, the LP function applying Newton had the lowest MPE (1.7\%) with the MG function applying an EA the highest MPE (4.1\%). Overall, minimal differences in MPE were observed when solving using the Newton and EA. However, the Newton method fixed some parameters values of the MG function to achieve approximately the same MPE as the EA which manipulated all parameter values. The results of this study illustrate that a MG function solved with an EA is an accurate and efficient way to model non-standard lactation curves but a LP function in combination with the Newton method canbe better option for more standard lactation curves},
	issn = {1176-5283},
	author = {Bryant JR and Lopez-Villalobos N}
}
@conference {41486,
	title = {Use of breeding values for live weight to calculate individual live weight targets for dairy heifers},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {64},
	year = {2004},
	month = {Jan},
	pages = {118-121},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Hamilton},
	abstract = {Replacement heifers need to reach specific target live weights (LW) to ensure they calve as two year olds, and subsequently achieve high milk yields and good fertility. Currently, different LW targets are recommended for heifers based on their expected mature LW according to appearance or breed. However, the mature LW is difficult to estimate without knowledge of the animals. genetic potential for LW. The objective of this paper is to develop and validate a growth model which uses estimated breeding values for LW (EBV LW) of individual heifers of any breed to calculate target LW from birth to maturity. Predicted live weights are presented for a range of four EBV LW, from {\textendash}40 to 100 kg. These values were very similar to other published target values. Data from the Dexcel Holstein Friesian Strain Trial was used to validate the model with respect to LW and age at puberty. For LW at puberty the predicted values were significantly correlated (P<0.05), but were marginally higher (3-5\%) than the actual values. A report can be formulated to enable farmers to identify individual heifers which are below (or above) their target LW at any date },
	issn = {1176-5283},
	author = {Bryant JR and Holmes CW and Lopez-Villalobos N and McNaughton LR and Brookes IM and Verkerk GA and Pryce JE}
}
@conference {41408,
	title = {Effect of genetic merit on the estimated partitioning of energy towards milk production or liveweight gain by Jersey cows grazing on pasture},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {63},
	year = {2003},
	month = {Jan},
	pages = {69-72},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Queenstown},
	abstract = {Data from the 1999/2000 season of the Stratford demonstration farm stocking rate trial was used to estimate metabolisable energy intakes (MEI) and the amount of metabolisable energy (ME) partitioned into milk, maintenance and liveweight (Lwt) changes of Jersey cows of either high genetic merit (HGM) (average milksolids breeding value of 28 kg) or low genetic merit (LGM) (average milksolids breeding value of 11kg). Least-square mean yields for HGM and LGM cows were 327 and 289 kg of milksolids per cow respectively. HGM cows partitioned a significantly higher proportion of MEI into milk than LGM cows in early (0.67 vs 0.63; P<0.01), peak (0.59 vs 0.57; P<0.05), mid (0.58 vs 0.56; P<0.01) and late lactation (0.54 vs 0.51; P<0.01) (HGM vs LGM respectively). In early lactation, HGM cows utilised more body reserves for milk production (-0.05 vs -0.01, for HGM and LGM respectively). These results confirm that HGM cows partition more ME to milk throughout lactation than LGM animals for a range of feeding levels on grazed pasture. The greatest difference occurred in early lactation, resulting in increased body tissue loss and a greater negative energy balance in HGM cows. },
	issn = {1176-5283},
	author = {Bryant JR and Lopez-Villalobos N and Holmes CW and Pitman GD and Brookes IM}
}
@conference {41409,
	title = {Evidence of a genotype by feeding level interaction in grazing Holstein-Friesian dairy cattle at different stocking rates},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {63},
	year = {2003},
	month = {Jan},
	pages = {73-76},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Queenstown},
	abstract = {Lactation yields and estimated breeding values (EBVs) for protein, fat and milk were obtained for individual cows in a farmlet trial carried out at Dexcel in Hamilton, using Holstein-Friesian cows, to test for the existence of a genotype by environment interaction across the range of feeding levels, and EBVs typically found on New Zealand pasturebased dairy farms. At very low levels of feeding, with yields of 267 - 307 kg milksolids per cow (kg MS/cow), regression coefficients of lactation yield on EBVs were not significantly different from the expected value of 1. At high levels of feeding, with yields of 383 - 411 kg MS/cow, most of the regression coefficients for yields of protein, fat and milk on EBVs were significantly greater than 1. The results of this study show that at low levels of feeding the actual differences in production between cows, which differ in EBVs correspond to the actual differences in EBVs, whereas at high levels of feeding the difference in milk yields between genetic groups are greater than the difference in EBVs. This constitutes a form of genotype x environment interaction, in which genotype is measured as breeding values, and has important practical and economic implications for dairy farms, and for the expected value of genetic improvements. },
	issn = {1176-5283},
	author = {Bryant JR and Holmes CW and Lopez-Villalobos N and MacDonald KA and Brookes IM}
}
