Effectiveness of whole linted cottonseed as a replacement for forage fiber in diets varying in starch availability
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Date
1999
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The Ohio State University
Abstract
Six primiparous Holstein cows (ruminally and duodenally cannulated) in a 6 x 6 Latin square design were used to determine the relationship between the physical effectiveness of whole linted cottonseed (WCS) and its level of forage substitution when diets varying in starch availability were fed. This relationship was evaluated based on stimulation of chewing activity, maintenance of milk fat percentage, intake, ruminal pH, and volatile fatty acid (VF A) concentrations. Diets were nutritionally equivalent; however, dietary composition differed in the amount of forage neutral detergent fiber (fNDF) supplied by alfalfa silage. Diets consisted of 1) high forage control with ground com (FCG; 21% fNDF); 2) 5% WCS with ground com (LCG; 18% fNDF); 3) 10% WCS with ground com (MCG; 15% fNDF); 4) 15% WCS with ground com (HCG; 12% fNDF); 5) 5% WCS with steam-flaked com (LCSF; 18% fNDF); and 6) 10% WCS with steam-flaked com (MCSF; 15% fNDF). Chewing activity (minutes/day) was unaffected by the level of WCS substitution for fNDF and com source. However, ruminating and total chewing activity per kg of fNDF intake quadratically increased (P<0.05) with level of WCS substitution. Even though milk fat percentage was similar between the FCG and LCG diets (3.67 and 3.69%), milk fat percentage tended to quadratically decrease with level of WCS substitution (P<0.05). Substituting steam-flaked com for ground com decreased milk fat percentage substantially (P<0.05). The addition of WCS to the diets quadratically increased (P<0.05) dry matter intake (DMI) and fNDF intake. However, replacing ground com with steam-flaked com decreased (P<0.05) DMI, neutral detergent fiber intake, and fNDF intake. Average nominal pH decreased linearly (P<0.05) as level of WCS substitution increased. Even though molar concentration of acetate in the rumen was unaffected by level of WCS substitution and com source, molar concentration of propionate in the rumen linearly increased (P<0.05) with level of WCS. Additionally, substituting steam-flaked com for ground com increased molar concentration of propionate (P<0.05). Lack of WCS x corn source interactions suggests that the effectiveness of WCS is not affected by availability of rumen degradable starch. Whole linted cottonseed is as physically effective as alfalfa silage at stimulating chewing activity in diets with at least 12% fNDF, but it is not as effective at maintaining milk fat percentage in diets with less than 18% fNDF.