Can the survival of lambs from larger litters be improved?

Abstract

Improved fecundity in sheep in the past 20 years has increased numbers of triplet lambs born on farm. The survival of triplet lambs is lower compared to single- and twin-born lambs, which raises welfare and wastage concerns and decreases farm profitability and sustainability. Three major factors that are known to influence survivability in triplet lambs are birthweights, thermoregulatory capacity, and behaviours at birth. These traits contribute to an increased risk of hypothermia, mismothering, starvation, and infection, especially in the first 3 days of life. Improving these traits and thus survival may be achieved through management practices, but how farmers manage triplet-bearing ewes and lambs, and whether their attitudes favour triplet lambs has not been investigated so far. Birthweight, thermoregulatory capacity, and lamb behaviours at birth may be influenced by effects of maternal nutrition during pregnancy on fetal growth and development; of which the placenta is a key regulator and facilitator of nutrient transport. However, how maternal nutrition influences placental nutrient transport, birthweight, thermoregulatory capacity, and behaviours in triplets is poorly understood. Research undertaken in this thesis explored both applied and fundamental research questions related to lamb survival in triplets. The three key objectives in this thesis were: to investigate factors that affect farm management practices and farmer attitudes towards managing triplet lambs; to understand the impact of placentome morphology and maternal arginine supplementation on placental nutrient transport capacity; and to investigate whether maternal dietary interventions from day 100 of gestation to birth can influence birthweight, thermoregulatory capacity, and neonatal behaviours in triplet lambs.

In the first study a quantitative questionnaire was offered online to sheep farmers from the United Kingdom (UK), Republic of Ireland (IRE) and New Zealand (NZ). There were substantial differences in farming system (indoor vs outdoor lambing), flock size, number of triplet lambs born in the most recent lambing season (2019) and management during pregnancy and around lambing. Differences in attitudes to cost, management and wanting triplets were present between countries, flock sizes and respondent age and gender groups. The results highlight that country of origin, flock size and farmer age and gender may dictate management practices on farm; hence adopting new strategies to improve lamb survival should focus on these factors.

The second study used archived caruncle and cotyledon tissue of type A, B and C placentome subtypes derived from a previous study in which 20 twin-bearing ewes had either received parenteral Arginine mono-hydrochloride (Arg) or saline (Ctrl). A panel of 31 genes involved in placental nutrient transport and placental function was investigated using Nanostring technology to measure gene expression. The results highlighted that placentome morphology changes are associated with differential expression of some specific amino acid transporter genes suggesting a potential adaptive response to increase the transport capacity of the placenta to support fetal growth. Supplementation (Arg versus Ctrl) influenced gene expression supporting amino acid transport, placental function, and angiogenesis, which may affect placental transport capacity. In the third study, triplet-bearing ewes were either fed a nutritionally balanced fodder beet dominant diet (FB), or a lucerne dominant (Ctrl) diet, each with or without oral N-carbamoylglutamate (NCG), an analogue which stimulates endogenous Arginine synthesis, in a 2x2 factorial design. Birthweight, rectal temperatures, and lamb- and ewe behaviours were measured in the first 24 hours post-birth. Diet (FB versus Ctrl) influenced birthweight, rectal temperature, blood parameters and lamb behaviours recorded at 1 hour after birth of the third-born lamb until 24 hours. Supplementation (NCG versus No NCG) influenced frequency of required birth assistance, blood parameters, rectal temperatures, and lamb behaviours. The results indicate that a very specific aspect of maternal nutrition influences these traits.

In summary, triplet lamb survival is an important welfare and profitability factor on sheep farms. The thesis describes novel effects of maternal nutrition on triplet lamb physiology and placental function that may contribute to future studies to improve triplet lamb survival. New insights into factors that influence management practices and attitudes towards triplet lambs will help develop targeted knowledge transfer strategies for management actions on farms.