Comparison of Mathematical Models Applied to F1 Dairy Sheep Lactations in Organic Farm and Environmental Factors Affecting Lactation Curve Parameter

Abstract

The objective of this study was to compare the goodness of fit of four lactation curve models: Wood’s Gamma model (WD), Wilmink (WL), and Pollott’s multiplicative two (POL2) and three parameters (POL3) and to determine the environmental factors affecting the complete lactation curve of F1 dairy sheep under organic management. A total of 5,382 weekly milk yields records from 150 ewes, under organic management were used. Residual mean square (RMS), determination coefficients (R2), and correlation (r) analysis were used as an indicator of goodness of fit for each model. WL model best fitted the lactation curves as indicated by the lower RMS values (0.019), followed by WD (0.023), POL2 (0.025) and POL3 (0.029). The four models provided total milk yield (TMY) estimations that were highly correlated (0.93 to 0.97) with observed TMY (89.9 kg). The four models under estimated peak yield (PY), whereas POL2 and POL3 gave nearer peak time lactation estimations. Ewes lambing in autumn had higher TMY and showed a typical curve shape. Higher TMY were recorded in second and third lambing. Season of lambing, number of lambing and type of lambing had a great influenced over TMY shaping the complete lactation curve of F1 dairy sheep. In general terms WL model showed the best fit to the F1 dairy sheep lactation curve under organic management.

The application of a mechanistic model to analyze the factors that affect the lactation curve parameters of dairy sheep in Mexico

“…Biological parameters of the Pollott model help us to explain the characteristics of lactation, predict appropriate milk yields and detect the systematic changes in yield caused by biological factors; this is in agreement with previous work in crossbred sheep (Angeles-Hernandez et al, 2013) and pure breeds like…”

“…As the lambing performance increases with age there is an improvement in the efficiency of homeorhetic dynamics involved in the partition of nutrients to the developing mammary gland and milk synthesis (González-García et al, 2015). Our results show an increase of TMY with lambing number, as previously (Angeles-Hernandez et al, 2013;González-García et al, 2015). The substantial difference of parameters that define the patterns of lactation curve and milk yield between lactation numbers are probably related to the biology of the mammary gland.. By interpreting the biological parameters from Pollott´s model, it can be established that the maximum TMY reached in third lambing is associated with lower decline in the udder cells (DR).…”

“…This mechanistic model mimics three processes that occur during pregnancy and lactation: differentiation of mammary secretory cells, programmed secretory cell death (apoptosis) and milk secretion cell per cell (Pollott, 2000). Pollott's model has been compared to empirical and mechanistic models of lactation curve fitting (Angeles-Hernandez et al, 2013;Elvira et al, 2013a;Pollott and Gootwine, 2000) and this model have been found to be the bestfit method using sheep's milk yield records; also, it has the advantage that it provides parameters which can have biological interpretation.…”

Effect of live weight pre- and post-lambing on milk production of East Friesian sheep

“…Several previous studies (Gootwine and Pollott 2000;Angeles-Hernandez et al 2013) reported a quadratic effect of the NL on milk production, point out that the lowest milk yields and more persistent lactation curves occur in the first lactation due to the mammary gland not being fully developed at the beginning of the first lactation (Abdelsayed et al 2015); afterwards, milk yields increase with the NL, showing the highest milk yields in the third and fourth lactation and a consequent decline until culling; this is in agreement with the results of the current study. An early study analysed the effect of the NL in milk production and BW of Chios sheep, stating higher milk yields in third lambing and maximum BWs in the fifth parity (Mavrogenis and Papachristoforou 2000); again, that coincides with our results.…”

Comparison of Different Lactation Curve Models to Describe Lactation Curve in Awassi Sheep Raised in Turkey

“…The environmental factors that affect the milk yield and lactation curve have been determined by many researchers, and different mathematical models have been proposed for determining the lactation milk yield in dairy cattle (Koncagül and Yazgan, 2011). Most of these models developed for dairy cattle can also be used to identify the lactation curves of sheep and goats (Fernandez et al, 2002;Koncagül et al, 2012;Angeles-Hernandez et al, 2013). Among them, Wood's model (1967) has been the most widely used (Nezamidoust et al, 2013;Angeles-Hernandez et al, 2013) Lactation curve studies have conducted rarely in Awassi sheep.…”