Level and quality of protein in rations for lactating ewes
Level and quality of protein in rations for lactating ewes
C Jaime 0 1
A Purroy 0 1
0 Navarra , Campus de Arrosadia s/n, 31006 Pamplona , Spain
1 Unidad de Producciôn Animal, Servicio de Investigacidn Agraria (DGA)), , Apartado 727, 50080 Zaragoza , Spain
Summary — The effect of 2 levels of crude protein in the ration (110 and 90% of theoretical requirements) and of 3 main protein sources in the concentrate (faba beans, soybean cake and fish meal) on changes in live weight and body condition score, milk production, plasma concentration of non-esterified fatty acids and urea, and lamb growth was studied in 36 lactating Rasa Aragonesa ewes rearing 2 lambs submitted to an energy restriction level of 30% of their theoretical requirements. The average decreases in live weight and body condition score of the ewes were not significantly affected by the two effects studied. The ewes that were given the higher protein level produced more milk, fat, protein, total dry matter and blood urea concentration than those that received the lower level (P< 0.05). A trend towards significance was observed in the maximum concentrations of non-esterified fatty acids according to the protein source (P=0.07). No significant differences were found in the results of lamb growth. protein / body condition I milk production / sheep / lambs Résumé — Niveau et qualité des protéines dans la ration des brebis en lactation. On a étudié chez 36 brebis Rasa Aragonesa allaitant2 agneaux, et ne recevant que 70% de leurs besoins énergétiques théoriques, l'effet de 2 niveaux de matières azotées totales dans la ration (110 et 90% des besoins théoriques) et de 3 sources de protéine dans l'aliment concentré (féveroles, tourteau de soja et farine de poisson), sur les changements de poids vif et de note d'état corporel, sur la production de lait, la concentration plasmatique d'acides gras non estérifiés et d'urée, ainsi que sur la croissance des agneaux. Les 2 effets étudiés n'ont pas modifié les pertes de poids vif et de note d'état corporel des brebis. Les mères avec le niveau le plus élevé de matières azotées dans la ration ont eu des productions de lait, de matière grasse, de matière azotée, de matière sèche totale et une concentration d'urée plasmatique plus élevées que celles avec un niveau plus bas (P < 0, 05). Une tendance vers la signification a été obser vée dans la concentration maximum des acides gras non estérifiés selon la source de protéine utilisée (P = 0,07). Il n'a pas eu de différences significatives dans la croissance des agneaux. protéine / état corporel / production laitière / brebis / agneaux
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The highest nutritional requirements of ewes
occur during the first 4-6 weeks of
lactation, when the energy and protein
requirements for milk production may be up to 3
and 4 times higher than for maintenance
(Robinson, 1988)
. During this period, the
ewes cannot consume all the food that is
necessary to meet their nutritional
requirements, and therefore must mobilize their
body reserves in order to compensate for
the dietary deficiency (MLC, 198 1).
For a specific level of ingested
metabolizable energy, the increase in the protein
content of the ration leads to a rise in milk
production when the ewe has not reached its
maximum milk production potential. This
response seems to be enhanced in ewes
with high restrictions in energy intake
(Robinson et al, 1974; 1979)
, although
positive responses have also been found with
energy intake close to the theoretical
requirements
(Gonzalez et al, 1984)
. This
phenomenon can be due either to a greater
mobilization of body reserves
(Robinson et
al, 1974)
or to an increase in the efficiency
of utilization of these reserves for milk
production (Cowan ef al, 198 1).
On the other hand, as the
degradability of dietary protein in the rumen
decreases, the amount of milk produced
by the ewe increases
(Robinson et al,
1979; GonzAlez et al, 1982)
. Only a small
part of the proteins exported in the milk
comes from body reserves (about 20%;
Cowan et al, 1981the rest comes from
the microbial proteins and from the dietary
protein that has not been degraded in the
rumen. Nevertheless, more recent results
do not show a strong relationship between
a lower degradability of protein and milk
production
(Penning et al, 1988; Ngongoni
et al, 1989; Hadjipanayiotou, 1992)
.
The present study investigates the effect
of the protein level in the ration and of the
quality of the protein source in the
concentrate on the yield and composition of the
milk of lactating ewes. The energy
requirements of these ewes are restricted to
stimulate the mobilization of body reserves. Data
are also presented for live weight, body
condition score and plasma concentration of
non-esterified fatty acids as indicators of
body reserve mobilization.
MATERIAL AND METHODS
Thirty-six lactating Rasa Aragonesa ewes, each
suckling 2 lambs, were used in this trial. They were
kept in individual pens under a regime of energy
i (...truncated)