Does grazing fodder beet during pregnancy affect lamb survival?
It is common practice to use brassicas to fill a feed deficit during winter when pasture growth rates are low. Traditionally brassicas such as swedes and kale have been largely used, however, there has been an increased use of fodder beet to fill the winter feed deficit.
Fodder beet is a crop (leaf and bulb combined) that has a high dry matter yield and low cost per unit of feed. It has high sugar, low crude protein and low fibre. However, there had been no research completed on how feeding fodder beet to pregnant ewes effects lamb production.
The objective of this study was to determine the effect of grazing fodder beet versus ryegrass pasture from mid-to-late gestation on ewe and lamb performance.
Fodder beet had greater dry matter, lower crude protein and lower neutral detergent fibre compared with Ryegrass pasture.
Ewes grazing ryegrass during pregnancy had greater live weight compared with ewes grazing Fodder beet.
Lambs born to ewes grazing Fodder beet had greater mortality from birth to weaning compared with lambs born to Ryegrass ewes.
Fodder beet has greater dry matter (DM) than ryegrass, 334 g/kg compared with 224 g/kg.
The estimated crude protein concentration of the fodder beet treatment offered was almost half that of the ryegrass treatment, 118 g compared with 224 g CP/kg DM.
In late pregnancy, multiple bearing ewes (those carrying more than one lamb) often struggle to consume enough feed and have higher protein requirements, this means that multiple bearing ewes grazing fodder beet may not be able to consume the required nutrients for late-pregnancy.
The authors mentioned that one limitation of the study was the inability to accurately estimate the feed intakes. So just remember the chemical composition of the feeds are an estimate only.
There were two treatments with 100 ewes in each
Fodder beet + hay
Ryegrass pasture + hay
Both treatments were not back fenced to allow for no intake restrictions.
Twin-bearing ewes were randomly allocated to a treatment from pregnancy day 100 to birth.
Ewe weight, body condition score change and lamb growth were measured. The graph below shows the average ewe live weight for each of the treatment groups, Ryegrass in purple and Fodder beet in blue. Compared with the Ryegrass treatment, the Fodder beet ewes had lower average daily growth rates, therefore, lower average live weight across pregnancy and lactation.
The ewes grazing fodder beet gained less weight than the ewes grazing ryegrass during pregnancy. This could indicate that the ewes grazing fodder beet were nutritionally restricted.
The Fodder beet treatment ewes also had lower body condition score compared with the Ryegrass ewes.
Lambs born to fodder beet ewes had lower birth weight 4.8 kg compared with 5.15 kg for the lambs born to ewes grazing ryegrass.
The graph below shows the mortality rate (% of lambs lost) between the Fodder beet and Ryegrass treatments. There was a significant difference in mortality between birth and 3 days old and between scanning and weaning.
Most lamb deaths often occur in the first 3 days after birth as a result of the effects of birthing difficulties and potential in utero issues.
There were 23% of lambs from the ewes that grazed fodder beet that did not survive to 3 days old compared with the 9% of lambs from ewes that grazed ryegrass.
There was only a slight increase in lamb mortality when the time period was extended out to weaning. There were 29% of lambs from the ewes that grazed fodder beet that did not survive to weaning compared with the 12% of lambs from ewes that grazed ryegrass.
Fodder beet, although a high yielding crop, in this study resulted in underfed ewes and therefore impacting on lamb growth and survival. It is probably best not to feed only fodder beet to multiple bearing ewes in mid to late pregnancy. Instead limiting fodder beet being fed to non pregnant or single bearing ewes.
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Hammond KJ, Sandoval E, McKenzie CM, Lees S, Pacheco D, McCoard SA. The effect of a fodder beet versus rye-grass grazing regime during mid-to-late gestation twin-bearing ewes on dam and progeny performance and lamb survival. New Zealand Journal of Agricultural Research. 2021 Feb 5:1-8.