Effects of sodium chloride on sheep. 2. Voluntary feed intake and changes in certain rumen parameters of young Merino wethers grazing native pasture

Abstract

While grazing native pasture, seven groups of 4 young Merino wethers received the following supplements daily via rumen cannulae: 0, 5 (Control), 15 and 30 g salt (NaCl); and 5, 15 and 30 g NaCl + 20 g crude protein (CP) each. There was a non-significant (P ≤ 0,05) tendency for digestible organic matter (DOM) intake to decrease with incremental levels of NaCl and to increase with CP supplementation (33,8; 34,5; 31,5; 31,3; 35,5; 35,8 and 31,3 g DOM / Wkg^0.75 day^-1). Although only some of the differences were significant (P ≤ 0,05), rumen pH tended to decrease with incremental levels of NaCl, as well as with CP supplementation (6,64; 6,58; 6,51; 6,59; 6,45; 6,51 and 6;25). CP supplementation had a significant (P ≤ 0,05) elevating effect and incremental levels of NaCl a non-significant (P ≤ 0,05) elevating effect on rumen NH₃ (4,72; 3,44; 3,51; 4,71; 7,74; 10,14 and 8,22 mg NH₃/100 ml rumen fluid). Volatile fatty acids (VFA) were, besides significant (P ≤ 0,05) differences in acetic acid between a few treatments, apparently not affected to any real extent by either NaCl or CP supplementation and the overall pattern of VFA proportions remained similar for all groups with an approximate ratio of
76:15:9. The tendency for CP to reduce ruminal Na was not significant (P ≤ 0,05), whereas the wethers receiving 0 g NaCl had a significantly (P ≤ 0,05) lower rumen Na concentration (1,367; 2,385; 2,876; 2,632; 1,674; 2,458 and 2,293 g Na l^-1). The wethers receiving 0 g NaCl had a significantly (P ≤ 0,05) elevated ruminal K concentration (2,821; 0,715; 1,031; 1,027; 0,747; 1,064 en 0,995 g K l^-1 ). Diurnal variations in rumen indices are also discussed. It is suggested that Na and K imbalances in the extra- and intra-cellular body fluid compartments, increased the maintenance energy expenditure of the wethers, thereby inducing the deleterious effects on production parameters.

Sewe groepe van 4 jong Merinohamels elk, het op veldweiding daagliks die volgende aanvullings via rumenkannules ontvang : 0, 5 (Kontrole), 15 en 30 g sout (NaCl); en 5, 15 en 30 g NaCl + 20 g ruproteïen (RP) elk. Daar was 'n nie-betekenisvolle (P ≤ 0,05) neiging vir die inname van verteerbare organiese materiaal (VOM) om te daal met toenemende NaCl-peile en om te styg met RP-aanvulling (33,8; 34,5; 31,5; 31,3; 35,5;
35,8 en 31,3 g VOM / Wkg^0.75 dag^-1). Die neiging vir rumen-pH om te daal met toenemende NaCl, sowel as met RP-aanvulling (6,64; 6,58; 6,51; 6,59; 6,45; 6,51 en 6,25), was slegs in enkele gevalle betekenisvol (P ≤ 0,05). Rumen-NH₃ was betekenisvol (P ≤ 0,05) hoër met RP aanvulling, maar het slegs hoer geneig met toenemende NaCl-peile (4,72; 3,44; 3,51; 4,71; 7,74; 10,14 en 8,22 mg NH₃/100 ml rumenvloeistof). Vlugtige vetsure (VVS) is, benewens betekenisvolle (P ≤ 0,05) verskille in asynsuur tussen 'n paar behandelings, skynbaar weinig geaffekteer deur beide NaCl- en RP-aanvullings. Die algemene verhouding van VVS vir die verskillende behandelings is naastenby op 76:15:9 gehandhaaf. Aanvullende RP het 'n nie-betekenisvolle (P ≤ 0,05) neiging getoon om rumen-Na-konsentrasie te verlaag, terwyl die hamels wat 0 g NaCl ontvang het, se rumen-Nakonsentrasie betekenisvol (P ≤ 0,05) verlaag is (1,367; 2,385; 2,876; 2,632; 1,674; 2,458 en 2,293 g Na l^-1). Die hamels wat 0 g NaCl ontvang het, het 'n betekenisvolle (P ≤ 0,05) hoër rumen-K-konsentrasie gehad (2,821; 0,715; 1,031; 1,027; 0,747; 1,064 en 0,995 g K l^-1). Daaglikse variasie in rumenparameters word ook bespreek.
Wanbalanse tussen Na en K in die ekstra- en intraselulêre liggaamsvloeistowwe, het waarskynlik die onderhoudsenergie-uitgawe verhoog, met die gepaardgaande nadelige effek wat in produksie waargeneem is.

Keywords: Crude protein, grazing sheep, NaCl, rumen parameters, supplementation, voluntary feed intake.