title: The effect of date of cut and barley substitution on gain and on the efficiency of utilization of grass silage by growing cattle. 2. Nutrient supply and energy partition.
abstract: 1. The effect of harvesting date of perennial ryegrass (Lolium perenne) on the nutritive value of the resultant silage and the effect of substitution of late-cut silage with barley was examined in growing cattle. The diets comprised early-cut (H) and late-cut (L) silage offered alone or with 280 (LC1) or 560 (LC2) g rolled barley/kg total dry matter (DM) substituted for late-cut silage. 2. Both silages were prepared with the addition of formic acid (850 milligram; 2.4 litres/t fresh weight) to a partially wilted crop, and were judged to be well fermented (pH 3.9, 3.8) with lactic acid contents of 108 and 73 g/kg DM, total nitrogen contents of 24.6 and 18.4 g/kg DM and ammonia-N contents of 121 and 124 g/kg total N (values for early- and late-cut silages respectively). 3. Two experiments were conducted to measure duodenal non-NH3-N (NAN) supply in relation to N intake on the four diets (feeding level 18 g DM/kg live weight (LW] and to examine the partition of the metabolizable energy (ME) supply from the four diets using open-circuit indirect calorimetry (three feeding levels, 14, 17 and 20 g DM/kg LW). The experiments were undertaken with eight and nine Friesian male castrates respectively with a mean starting weight of 300 kg and age 12 months. The animals used in Expt 1 had been previously fitted with cannulas into the dorsal rumen and the proximal duodenum. 4. NAN supply was significantly higher on diet H than all other diets which were similar irrespective of the level of barley inclusion. Mean ME contents (MJ/kg DM) of the two silages differed markedly (H 11.9, L 9.7) and barley addition (LC1 and LC2) restored values to 10.7 and 11.1 MJ/kg DM respectively. Estimated NAN absorption in relation to energy supply was significantly higher for diet H (1.47 g/MJ ME) than for all other diets (mean 1.25 g/MJ ME). 5. Partition of ME supply using conventional linear analysis indicated dietary differences with respect to estimated ME for maintenance (L greater than H, LC1 and LC2) and efficiency of utilization of ME supplied above maintenance (L greater than H, LC1 and LC2), but difficulties in biological interpretation of these findings led to the use of exponential curve analysis. This provided an improved description of the findings, and whilst dietary differences were apparent, none were statistically significant. It was concluded that a single exponential equation could be used satisfactorily to describe all values.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: AFRC Institute for Grassland and Animal Production, Maidenhead, Berkshire.
authors.forename: D E
authors.initials: DE
authors.lastname: Beever
authors.forename: S B
authors.initials: SB
authors.lastname: Cammell
authors.forename: C
authors.initials: C
authors.lastname: Thomas
authors.forename: M C
authors.initials: MC
authors.lastname: Spooner
authors.forename: M J
authors.initials: MJ
authors.lastname: Haines
authors.forename: D L
authors.initials: DL
authors.lastname: Gale
mesh_terms: D000821:Animal Feed; D000818:Animals; D001835:Body Weight; D002151:Calorimetry; D002417:Cattle / Q000378:metabolism*; D004044:Dietary Proteins / Q000032:analysis; D004386:Duodenum / Q000378:metabolism; D004734:Energy Metabolism; D005243:Feces / Q000032:analysis; D001467:Hordeum; D007408:Intestinal Absorption; D008297:Male; D009584:Nitrogen / Q000032:analysis; D006109:Poaceae; D012820:Silage; D013997:Time Factors
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen