@conference {41738,
	title = {Evaluation of a model that estimates insulin sensitivity in dairy cows},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {67},
	year = {2007},
	month = {Jan},
	pages = {261-265},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Wanaka},
	abstract = {Glucose challenge data was used to model parametersdescribing the dynamics of the glucose-insulin system such as glucose effectiveness (SG), acute insulin response to glucose (AIRg) and insulin sensitivity (SI) in dairy cows. The relationship of these parameterswith post-partum anovulatory interval (PPAI) was also determined. Twenty-five HF cows of New Zealand (NZ; n=13) and Overseas (OS; n=12) origin, were fed either pasture (n=12) or a total mixed ration (TMR; n=13) in a 2x2 factorial design. At two weeks postpartum, they were challenged intravenously with 300 mg of glucose/kg live weight. There was no effect of diet on SG(P=0.302), SI(P=0.17) or AIRg(P=0.093) despite TMR cows of both genotypes having higher values. There was no effect of genotype on SG(P=0.234), SI(P=0.742) or AIRg(P=0.385). Correlations of these parameters with PPAI were not statistically significant: SI  (r 2=0.087, P=0.310), SG(r 2 = 0.001,  P=0.962) and AIRg(r 2 =0.036, P=0.320). Use of this model demonstrated that insulin response parameters  were not closely associated with PPAI.},
	issn = {1176-5283},
	author = {Back PJ and Boston RC and Palliser CC and Kolver ES and Chagas LM}
}
@conference {41989,
	title = {Restricted postpartum feeding in grazing dairy heifers decreases milk production but does not lengthen oestrous interval},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {67},
	year = {2007},
	month = {Jan},
	pages = {255-260},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Wanaka},
	abstract = {The aim of this study was to determine the effects of pasture allowance postpartum on the initiation of ovarian activity, metabolite and hormonal secretion, and milk production. After calving, thirty six HolsteinFriesian heifers (BCS 5.0) received either unrestricted pasture allowance (UNR; n=18) or restricted (RES; 73\% dry matter intake of the unrestricted group;n=18) pasture allowance. The LW was lower (P < 0.05) for the RES group than the UNR group. Body condition score of all heifers decreased after calving in both groups. The mean time to ovulation was similar for UNR 50.0 and RES 50.3 sed. 8.2 days after individual calving date. The daily average from week 2 for milksolids, protein and lactose yield was lower (P < 0.05) in the RES group. Plasma concentrations of insulin were lower (P = 0.0085) in the RES group when compared to the UNR group. Glucose concentrations was lower (P = 0.016) in the RES group. Plasma concentration of NEFA was greater (P = 0.001) in the RES group. There was an interaction with treatment differences decreasing by week 11 and 12 for glucose (P =0.001) and NEFA (P =0.006). Plasma concentrations of leptin (P = 0.013) and IGF-I (P = 0.026) were lower in the RES. No differences, associated with postpartum nutrition, were found for plasma GH. Restricted feeding postpartum had no effect on days to first postpartum ovulation but decreased liveweight, milk production and affected some metabolic hormones during postpartum.},
	issn = {1176-5283},
	author = {Chagas LM and Gore PJS and MacDonald KA and Blache D}
}
@conference {41670,
	title = {Diet or strain: Effects on postpartum anovulatory interval in dairy cows},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {66},
	year = {2006},
	month = {Jan},
	pages = {339-343},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Napier},
	abstract = {Changes in cow genetics and systems of farming have had large effects on the reproductive performance of dairy cows. The objective of this study was to determine if grain supplementation modified the previously identified effects of Holstein-Friesian (HF) strain on the postpartum anoestrus interval (PPAI). Thirty multiparous Overseas (OS) HF and 30 New Zealand-HF cows from a 1990s strain (NZ) were offered unrestricted access to fresh pasture and randomly allocated to three levels of a maize and barley-based concentrate supplementation (0, 3 or 6 kg DM/day). Postpartum anovulatory interval (PPAI) was not significantly affected by either strain or diet, and there was no significant strain x diet interaction. Results suggest that the nutritional requirements necessary for multiparous NZ or OS HF cows to resume oestrous cycles before 40 days postpartum can be achieved when offered unrestricted access to high quality pasture. In this circumstance, additional concentrate feeding did not alter the length of the postpartum anoestrous interval. },
	issn = {1176-5283},
	author = {Chagas LM and Gore PJS and Sheahan AJ and Lee JM and Watkins KA and Aspin PW and Roche JR}
}
@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 {41471,
	title = {Efficacy of pre-mating supplementation with mono propylene glycol on reproductive performance of cows in commercial dairy herds},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {64},
	year = {2004},
	month = {Jan},
	pages = {53-57},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Hamilton},
	abstract = {Prolonged postpartum anoestrous intervals (PPAI) are the major source of infertility in New Zealand dairy cows. Postpartum supplementation with mono propylene glycol (MPG) was previously shown to reduce PPAI in heifers. The present experiment tested this treatment in four large commercial dairy herds. During the six-week period preceding the planned start of mating (PSM; week 0), cows were drenched either once (1xMPG) or twice (2xMPG) daily with 200 ml MPG, or served as untreated controls (CON). Analyses were confined to the group of cows that were anoestrus at Week {\textendash}6 or calved between Week {\textendash}6 and Week {\textendash}4 relative to PSM (n = 662 to 669 per treatment). Change in body condition score between Week {\textendash}6 and Week {\textendash}1(∆BCS), and proportion of cows that were anoestrus at Week {\textendash}1 were influenced by herd, age and time of calving (P<0.05) but not by treatment (P>0.1). Treatment did not influence the proportion of anoestrous-treated cows inseminated after oestrus detection (n =263), or the pregnancy rate among all cows. Pre-mating supplementation with MPG did not influence ∆BCS, the percentage of cows that were anoestrus at Week {\textendash}1, or rates of submission and conception. Change in BCS affected both milk yield and pregnancy rates, where cows that gained BCS produced less milk but showed higher 6-week pregnancy rates. This study highlighted that key factors influencing the percentage of anoestrus at PSM are cow age, time of calving and management of the herd. },
	issn = {1176-5283},
	author = {Tunon GE and Taufa VK and Burke CR and Holmes CW and Chagas LM}
}
@conference {41399,
	title = {Metabolic responses to glucose challenge in New Zealand and overseas Holstein-Friesian dairy cows},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {63},
	year = {2003},
	month = {Jan},
	pages = {31-34},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Queenstown},
	abstract = {North American and Dutch Holstein-Friesian (HF) cattle have undergone genetic selection for increased milk production, however, at the same time, reproductive efficiency has decreased. Overseas HF also have greater propensity to mobilise body reserves during early lactation than New Zealand HF cows. It is possible that reproductive differences are a consequence of metabolic and endocrine differences between the strains. This trial was designed to investigate effects of genotype and diet on endocrine response to a challenge of intravenous glucose in HF cows. Twenty-five HF cows of New Zealand (NZ; n=13) and Overseas (OS; n=12) origin, were fed either pasture (Grass; n=12) or a total mixed ration (TMR; n=13) in a 2x2 factorial design. At two weeks postpartum, they were challenged with 300mg of glucose/kg live weight. Data were analysed for effects of genotype and diet. Following glucose challenge, the NZ TMR cows had higher plasma insulin concentrations than the NZ Grass, resulting in a significant interaction between diet and genotype in the area under the response curve; but the OS groups had similar patterns. Mean plasma leptin concentration was higher in NZ TMR than in NZ Grass, OS TMR or OS Grass. Plasma concentrations of glucose and IGF-I were not affected by genotype or feed regime. These results demonstrated metabolic differences between the strains and also diets. A better understanding of the genetic and nutritional basis of hormonal regulation of nutrient partitioning will be important to develop nutritional strategies to meet the requirements of lactating cows with different genotypes, and to find ways to improve reproductive efficiency. },
	issn = {1176-5283},
	author = {Chagas LM and Clark BA and Rhodes FM and Blache D and Kolver ES and Verkerk GA}
}
@conference {41309,
	title = {Effect of body condition at calving of milkfat composition of Friesian heifers during the first ten weeks of lactation},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {62},
	year = {2002},
	month = {Jan},
	pages = {38-41},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Palmerston North},
	abstract = {The effects of live weight and body condition score (CS) at calving on milksolids production has been well documented. The effects of CS at calving on detailed composition of milk, the physical characteristics, or, product quality are largely unknown. Milkfat yield, fatty acid profile (FAP), solid fat content (SFC) of milkfat during the first 10 weeks of lactation were monitored for Friesian heifers with a pre-calving CS of 4.1 (LCS) or 5.2 (HCS). Once calved, all heifers were grazed as one herd and offered pasture ad libitum. Composition and characteristics of milkfat were determined at four, six, and 10 weeks postpartum. At four weeks postpartum the HCS heifers, produced 23\% more (P<0.001) milkfat, lost 59\% more (P<0.001) live weight and CS declined 30\% more (P<0.05) than did LCS heifers. Associated with these changes were compositional changes in milkfat. CS at calving had no effect on milkfat concentration. HCS heifers produced milkfat with lower concentrations (P<0.01) of de novo synthesised fatty acids (C4:0-C15:1) and higher (P<0.01) concentrations of preformed fatty acids. Concentration (mg/100 mg milkfat) of oleic acid (C18:1) was higher: 27.4\% c.f. 24.8\%, s.e.d. 0.94 (P<0.001) for HCS compared with LCS heifers. Milkfat from HCS heifers was softer, SFC at 5{\textdegree}C (55\% c.f. 59\%, s.e.d. 1.2, P<0.01) than from LCS heifers. Six weeks postpartum, the differences in FAP persisted but changes in live weight and CS were small compared with the first four weeks of lactation. Ten weeks post calving both groups were gaining live weight, but although differences (P<0.01) in live weight, CS, and daily milkfat yield persisted, no differences in FAP or SFC were found. These results show that differences in pre-calving live weight and CS cause differences in the composition and characteristics of milkfat. Milkfat from HCS heifers was more desirable (softer and higher in unsaturated fatty acids) than from LCS heifers. These differences disappeared once the two heifer groups were in positive energy balance by 10 weeks postpartum. },
	issn = {1176-5283},
	author = {Thomson NA and Bryant MO and Chand A and MacGibbon AKH and Chagas LM}
}
@conference {41282,
	title = {Postpartum anoestrous interval and metabolic changes in heifers supplemented with pasture prepartum},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {61},
	year = {2001},
	month = {Jan},
	pages = {188-191},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Christchurch},
	abstract = {The aim of this study was to determine whether supplementation with pasture from 6 weeks before calving would alter the postpartum anoestrous interval (PPAI) in heifers calving with low body condition score (BCS). Metabolic hormones and metabolites were measured during the pre- and postpartum period. Forty Friesian heifers were managed during the last five months of gestation to achieve a BCS (1-10) of 4.0 (restricted; R; n=27) or 5.0 (fully fed; FF; n=13) by 6 weeks prepartum. One group with low BCS then received pasture ad libitum until calving (restricted + fully fed; R+FF; n=12). Live weight (LW) and BCS were assessed weekly. Blood samples were collected weekly from 10 weeks prepartum to 10 weeks postpartum to measure glucose, urea, non-esterified fatty acids (NEFA), betahydroxybutyrate (BOH) and cholesterol content. The patterns of metabolites measured differed between groups at different times, future work to investigate the relationship these profiles and PPAI would be of value. The percentage of cows cycling as measured by an elevated milk progesterone concentration was 69\%, 75\% and 8\% for FF, R+FF and R groups, respectively. Fully feeding heifers, with low condition score, 6 weeks before calving decreased PPAI when compared to heifers receiving restricted feeding. },
	issn = {1176-5283},
	author = {Chagas LM and Morgan SR and Gore PJS and Clark BA and Verkerk GA}
}
@conference {41148,
	title = {Prediction of post-partum anovulatory interval in dairy cows},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {60},
	year = {2000},
	month = {Jan},
	pages = {15-18},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Hamilton},
	abstract = {Changes in a range of metabolites and body condition parameters in lactating cows were measured during early lactation to determine if any key indicators or combination of key indicators could be used as a predictor of length of post-partum anovulatory interval (PPAI). Fifty-three cows in a range of body condition scores were involved in the trial which ran from calving to 10 weeks post-calving. Plasma non-esterified fatty acids (NEFA) and serum cholesterol, glucose, betahyroxybutyrate (BOH) and urea content were measured in weekly samples. Live weight and body condition score (BCS) were measured weekly.Cows were categorised into four groups. Three groups were based on the post-partum anovulatory interval (PPAI). PPAI was defined as the interval between calving and the first evidence of oestrus behaviour. The fourth group contained all the two-year-old cows only. There was a calving interval of 31 days from the first to the last cow to calve. The nadir for live weight for all groups occurred one week after calving. Animals with a shorter PPAI had higher live weights on all occasions, with live weight at week 5 having the strongest association with length of PPAI (P<0.001). Mean BCS was higher for animals with a PPAI<60 days. Plasma urea concentrations were associated with PPAI at weeks 3 and 4 (P<0.01). NEFA and glucose were correlated with PPAI at weeks 3 and 4 only, respectively. There was no association between cholesterol or BOH with PPAI. These results demonstrate that the selected variables do not contribute greatly to prediction of PPAI. Those measures which give the closest association with PPAI are live weight, BCS and age. },
	issn = {1176-5283},
	author = {Clark BA and Chagas LM and Gore PM and Dow B and Verkerk GA}
}
