Ruminal protein and fibre degradability of lucerne hay as affected by regrowth period and dairy breed

Cw Cruywagen,Fj Du Toit,Cjc Muller

doi:10.4314/sajas.v41i4.9

Abstract

The chemical composition of roughages constantly changes while it grows towards maturity. The effective dry matter (DM), crude protein (CP) and neutral detergent fibre (NDF) degradabilities of lucerne hay (LH), harvested after regrowth periods of 4, 5 or 6 weeks, were determined in ruminally cannulated Holstein and Jersey cows by using the in sacco nylon bag technique. The degradabilities of DM and NDF across breeds differed between the LH harvested after the regrowth periods of 4, 5 and 6 weeks. Increasing the regrowth period of LH from 4 to 6 weeks significantly reduced effective DM degradability (k p = 0.08) from 59.0% to 51.2% and NDF degradability from 30.8% to 21.2%. Crude protein degradability tended to decrease with advancing maturity, with values of 77%, 73% and 74% after 4, 5 and 6 weeks’ regrowth, respectively. Effective degradability of DM, CP and NDF did not differ between Holstein and Jersey cows. The results from this study suggest that LH harvested after a shorter regrowth period is of a higher quality in terms of DM, CP and NDF degradability which decreases as the plants mature. Keywords: Nutrition, forage, Holstein and Jersey cows, alfalfa

Highlights

Forage quality is a complex interrelationship of factors that affects the potential feed intake, nutrient content, digestion, gut fill and passage rate in ruminants (West, 1998)
The crude protein (CP) content of the lucerne hay (LH) used in the current trial (Table 2) was higher than the values indicated in the NRC (1989) tables for LH in the late vegetative, early blooming and mid-blooming growth stages
The CP content of the LH harvested after the regrowth periods of 4, 5 and 6 weeks agree with values reported by Gray (2001) for LH described as late budding, early blooming and blooming stages, viz. 217, 192 and 176 g/kg, respectively

Summary

Introduction

Forage quality is a complex interrelationship of factors that affects the potential feed intake, nutrient content, digestion, gut fill and passage rate in ruminants (West, 1998). The harvesting stage is the main factor which affects the nutritive value of forages (Linn & Martin, 1989). Harvesting LH at an early (immature) growth stage, results in high quality forage but in a low DM yield, while delayed harvesting has the opposite effect (Orloff, 1999). The leaf to stem ratio contributes significantly towards the quality of the lucerne no matter whether it is preserved as hay or silage, because the leaves contain 60% of the total digestible nutrients (TDN), 70% of the crude protein (CP) and 90% of the vitamins (Vough, 2001). The negative effects associated with LH, harvested at a more mature growth stage, have cost implications for dairy farmers. Feeding a lower quality LH in dairy cow diets necessitates the inclusion of more concentrates to provide sufficient energy and protein in the total diet, increasing the feeding cost

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