@conference {41843,
	title = {Mathematical modelling of anoestrus in dairy cows and the linkage to nutrition},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {65},
	year = {2005},
	month = {Jan},
	pages = {324-328},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Christchurch},
	abstract = {Postpartum anoestrus is a major reproductive problem in New Zealand dairy cows and its duration is related to the nutrition levels both pre and post calving. However, the mechanistic details of this relationship are largely unknown. A better understanding of the interactions between nutritional status, and the levels of the reproductive hormones controlling follicle development and ovulation is needed. A mathematical model consisting of a set of interactive nonlinear differential equations and describing the dynamics of the interactions among luteinising hormone (LH), follicle stimulating hormone (FSH) and oestradiol was developed. The model depicts oestradiol profiles generated by individual follicles from the first follicular wave after calving until ovulation, and changes in LH pulsatility leading to the first pre-ovulatory surge are also produced. The robustness of the model was ascertained from iterative processes, and it was also checked against existing experimental data so as to mimic observed changes in hormone levels. It was shown that two mathematical parameters which control: i) the speed of changes in the feedback of LH activity to oestradiol; and, ii) the sensitivity of the ovarian response to LH, have the greatest effect on duration of anoestrus.
KEYWORDS: mathematical model; anoestrus; dairy cows; nutrition; oestradiol; LH; FSH. },
	issn = {1176-5283},
	author = {Smith JF and Soboleva TK and Peterson AJ and Pleasants AB and Chagas LM and Burke CR}
}
@conference {41844,
	title = {Relationships among metabolic hormones, luteinising hormone and anoestrus in periparturient dairy heifers fed two nutritional levels prepartum},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {65},
	year = {2005},
	month = {Jan},
	pages = {329-334},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Christchurch},
	abstract = {A mathematical model that describes the dynamics of reproductive hormones was developed to estimate the duration of the postpartum anoestrus interval (PPAI) in cows. The model identified two relatively separate mechanisms: one influenced PPAI through luteinising hormone (LH) release; and it is suggested that another one controlled ovary sensitivity to LH. Examining the role played by these mechanisms in the relationships between nutrition and PPAI involved analysing the data from an experiment that measured the effects of prepartum nutrition on PPAI in which levels of insulin-like growth factor-I (IGF-I), insulin, glucose, leptin and growth hormone (GH) were recorded. Five months before calving, 30 Holstein-Friesian heifers were randomly allocated to a high (HP) or low plane (LP) of nutrition. Body condition scores at calving were 6.3 and 4.1 for the HP and LP treatments respectively. Both groups were fed ad libitum after calving. Secretion patterns of LH were measured at 2, 5 and 8 weeks after calving. PPAI differed between treatments (HP 62.0 {\textpm} 7.95 days; LP 83.1 {\textpm} 6.95 days; P < 0.05), as did the level of GH at calving (HP 5.8 {\textpm} 1.23 ng/ml; LP 10.3 {\textpm} 1.23 ng/ml; P < 0.001). The within treatment variation in PPAI was partitioned into that associated with LH frequency post calving and that orthogonal to LH pulse frequency. Within each treatment, GH was associated with the LH frequency and insulin was associated with the component orthogonal to LH frequency. These results link nutrition to the PPAI through the dynamics of insulin and GH.
KEYWORDS: mathematical model; anoestrus; dairy cows; nutrition; metabolites; LH. },
	issn = {1176-5283},
	author = {Pleasants AB and Chagas LM and Burke CR and Smith JF and Soboleva TK and Peterson AJ}
}
@conference {41296,
	title = {Modelling the impact of milking frequency on lactation},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {61},
	year = {2001},
	month = {Jan},
	pages = {239-240},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Christchurch},
	abstract = {Increasing milking frequency from the usual practice of twice-daily can enhance milk production and, thus, may be profitable in high-intensity dairy production systems. A decrease of milking frequency to once-daily decreases yield but may be used to alleviate nutritional stress, to conserve cow condition, or simply as a lifestyle choice. Published values in the literature indicate that reducing milking frequency from twice daily to once daily decreases yield by 7{\textemdash}34\%, and increasing milking frequency from twice daily to thrice daily increases yield by 7{\textemdash}20\% (Davis et al., 1999; Stelwagen, 2001). Additionally, milking frequency can influence the rate of decline in post-peak production in cows (Stelwagen, 2001).
In order to further understand and quantify the manner in which milking frequency affects lactation, a mechanistic mathematical model of mammary function has been developed (Vetharaniam, Davis, Soboleva, Shorten \& Wake, Unpublished), based on mechanisms presented by Davis et al. (1999). As well as allowing analysis of the effect of milking frequency, this model also facilitated the exploration of some of the pathways through which nutrition influences mammary gland development (Davis et al. 2001). },
	issn = {1176-5283},
	author = {Vetharaniam I and Davis SR and Soboleva TK and Shorten PR and Wake GC}
}
@conference {41140,
	title = {A Dynamical Model of Body Composition in Sheep},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {59},
	year = {1999},
	month = {Jan},
	pages = {275-278},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {A dynamical model describing the evolution of muscle, viscera and fat in response to different levels of energy intake over time in sheep is presented. The model shows responses consistent with observations of compensatory growth in sheep and cattle over a range of energy intake levels. Model parameters are derived from data measured by Ferrell et al., (1986) to investigate compensatory growth in lambs. The model is shown to generally reproduce the behaviour of the muscle, viscera and fat components of the lambs in this trial. The utility of the model for designing optimal nutritional management strategies for raising animals for slaughter is discussed, as well as the potential of the model to advance the understanding of animal nutrition by investigating different functional forms for relationships such as maintenance requirements. },
	issn = {1176-5283},
	author = {Soboleva TK and Oddy VH and Pleasants AB and Oltjen JW and Ball AJ and McCall DG}
}
