Modelling of normal and extended lactation for milk, fat and protein yields of New Zealand dairy goats : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Palmerston North, New Zealand
Loading...
Files
Date
2023
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
The use of extended lactation has been introduced as a management practice to minimise the high number of surplus young born in the dairy industry while still meeting the growing demand for high milk yields (MY) worldwide. Extended lactation has been looked at previously in dairy cows globally and in New Zealand. While extended lactation in dairy goats has only been studied overseas, not in New Zealand. Therefore, this thesis aims to investigate whether extended lactation could be employed as a future management practice in New Zealand dairy goat farming. To achieve this, the main objective of this thesis was to model and compare MY, fat yield (FY) and protein yield (PY) data collected from New Zealand dairy goats in extended lactation (670d) with goats in normal lactation (270d). The influence of pregnancy, parity number, lactation year and the month starts lactation was explored. The data analysed were collected from a large commercial farm in Waikato, New Zealand. The main findings suggest that extended lactation would be a beneficial management practice for New Zealand Dairy goat farms. This thesis discovered that New Zealand dairy goats in extended lactation produced a higher average total MY (657.24 kg higher), FY (16.7 kg higher) and PY (22.63 kg higher) than goats in two normal lactations. This likely reflects the effect of an absence of a dry period for extended lactation and/or the effect of pregnancy on a normal lactation. Indeed, the present results illustrated an effect of pregnancy, as when goats in normal lactation were dried off after 270 days their average on day 270 was only 2.81 kg (c.f., 3.35 kg for goats in extended lactation at this time). Milk production for both normal and extended lactations were also affected by parity, lactation year and lactation start month. All goats’ MY, FY and PY increased from parity one to peak at parity three or four, before gradually declining thereafter. For lactation year, all three yields increased from 2013 until 2019, most likely representing genetic gain. The lactation start month with the lowest yields for normal and extended lactation goats was June, with peak yields occurring for normal and extended lactations starting in August and September, respectively. This was likely due to an effect of photoperiod or feed availability on milk production. Ultimately, this thesis supports extended lactation as a beneficial management practice in New Zealand dairy goat farms as there was greater milk production than by normal lactation goats and reduced surplus offspring. Further studies are required to determine the effect of extended lactation on other milk components, farm profitability and goat health.
Description
The following Figures were removed for copyright reasons: Figs 2.1 (=Pulina et al., 2018 Fig 1b); 2.3 (=Salama et al., 2005 Fig 1); 5.1 (=Aboul-Naga et al., 2012 Fig 1). Fig 2.2 was reused under a Creative Commons Attribution 4.0 International (CC BY 4.0) license.