Lifetime changes in wool production of Merino sheep following differential feeding in fetal and early life
R. W. Kelly A B D , J. C. Greeff A and I. Macleod A CA Department of Agriculture and Food WA, Locked Bag 4, Bentley Delivery Centre, Bentley, WA 6983, Australia.
B Present address: CSIRO Livestock Industries, Private Bag 5, Wembley, WA 6913, Australia.
C Department of Primary Industries, PIRVic, 475–485 Mickleham Road, Attwood, Vic. 3049, Australia.
D Corresponding author. Email: rob.kelly@csiro.au
Australian Journal of Agricultural Research 57(8) 867-876 https://doi.org/10.1071/AR05312
Submitted: 22 September 2005 Accepted: 27 February 2006 Published: 9 August 2006
Abstract
In commercial Merino farming, a major determinant of profitability is quantity and quality of wool production. We tested the hypothesis that the level of feed restriction commonly encountered by autumn/early winter lambing Merino ewes in southern Australia was sufficient to have a detrimental effect on their progeny’s lifetime wool production. Two periods of feed restriction of the dams were tested, viz. from day 50 to 140 of gestation (Expt 1), and from day 50 of pregnancy to weaning at 12 weeks of age (Expt 2). In order to reduce the numbers of experimental animals required, identical twin lambs were produced by cloning embryos. There was a total of 35 and 22 pairs of clones in Expts 1 and 2 that were recorded to 6.4 and 4.4 years of age, respectively. In Expt 1 it was estimated (i.e. conceptus-free weight) that the submaintenance (Sub-M) ewes lost 18 kg in weight compared with 9 kg by the Control (C) ewes over the period of differential feeding. In Expt 2 the Sub-M ewes lost 10 kg during pregnancy and 10 kg during lactation, compared with a loss of 3 kg and a gain of 4 kg over the same period in the C ewes. Gestation length was 1.3 days shorter (P < 0.01) in the Sub-M than C ewes in Expt 1. Birthweights of the Sub-M lambs were 0.5 kg lighter than the C lambs in Expts 1 (P < 0.01) and 2 (P < 0.05). At 12 weeks of age, liveweights of the lambs in the Sub-M and C treatments were 24.2 and 25.9 kg in Expt 1 (P < 0.01) and 14.0 and 25.0 kg in Expt 2 (P < 0.001). Corresponding liveweights at 4 months of age were 30.9 and 32.5 kg (P < 0.01) and 19.9 and 29.7 kg (P < 0.001), the Sub-M animals producing less clean wool (0.1 and 0.4 kg, P < 0.01 and < 0.001, Expts 1 and 2, respectively), that was finer in Expt 2 (2.7 μm, P < 0.001) than their C counterparts.
Throughout the rest of the study the Sub-M animals in Expt 2 (but not Expt 1) were on average 3.2 kg lighter (P ranging from < 0.05 to < 0.001) than C animals. In both experiments the ratio of secondary to primary wool-producing follicles was lower (1.1–2.6 units, P < 0.001) in the Sub-M than C animals. These differences led to (P < 0.05) lower significantly adult clean wool production of 0.17 kg (Expt 1) and 0.24 kg (Expt 2) per annum. There was no significant interaction between nutritional treatment and age of the animal for clean wool production. Within experiments there were no significant differences between nutritional treatments in any of the wool quality measurements. However, when fibre diameter data for both experiments were combined for 3.4 and 4.4 years of age, the Sub-M animals were significantly broader (0.3 μm, P < 0.01) when compared with the C animals. We conclude that Sub-M feeding of the pregnant ewe will permanently affect liveweight, the wool follicle population, and wool production and quality, in Merino sheep. Extension of the period of under feeding into lactation (Expt 2) appears to increase the amplitude of the differences in young animals, which is largely overcome by the time the animal reaches 2.4 years of age.
Additional keywords: fetal programming, undernutrition, wool, growth.
Acknowledgments
We acknowledge the financial support of the Australian Wool Research and Promotion Organisation, now known as Australian Wool Innovation, for those years when the cloned progeny were being produced.
Over the duration of the experiment, many people were involved in assisting at various times, for which we are extremely grateful. In particular, we wish to acknowledge the skilled contribution made by farm staff of the Western Australian Department of Agricultures Great Southern Agricultural Research Institute, and the technical assistance of Mark Richardson, Annie Lewis, Peter Newton, Robyn Pitman and Robyn Bradley. Myra Yelland and John Davies provided outstanding technical support for this project through to its completion. Our research colleagues included Andras Széll, Roger Lewer, David Windsor, and Phil Hynd.
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