Body weight and sex effects on digesta mean retention time in growing Saanen goats

Despite the important role of digesta mean retention time (MRT) on digestive efficiency of ruminants, it is poorly investigated in total gastrointestinal tract (GIT) of growing ruminants, especially in goats. The objective of this study was to evaluate the effect of body weight (BW) and sex on GIT MRT of particles and solutes in growing Saanen goats. A dataset from two studies, comprising 103 individual records of castrated males (n = 36), females (n = 34), and intact males (n = 33) Saanen goats slaughtered at 15, 22, 30, 37, and 45 kg BW, was used. Goats were fed basically with total mixed ration composed by dehydrated corn plant (Zea mays) milled to pass a 10-mm screen, cracked corn grain, and soybean (Glycine max) meal. Variables evaluated were BW, feed intake, feed intake level, composition of ingested diet, wet weight of GIT tissues, wet digesta pool size, digesta composition (dry matter and neutral detergent fiber [NDF]), indigestible NDF:NDF ratio of ingested diet and GIT digesta, MRT of particles (MRT(iNDF)) and solutes (MRT(Cr)), and reticulorumen selectivity factors (large particles/solutes). Reticulorumen, omasum, abomasum, small intestine, cecum, and colon–rectum segments were evaluated. The dataset was analyzed as mixed models considering sex, BW, and sex × BW interaction as fixed effects, and study and residual error as random effects. Sex did not affect MRT(iNDF) in any GIT segments. Females and intact males presented similar reticulorumen MRT(Cr) (5.6 h; P = 0.92) and they presented lower reticulorumen MRT(Cr) than castrated males (7.0; P ≤ 0.04). Total GIT MRT(Cr) was similar between castrated males and females (15.7 h; P = 0.11) and between females and intact males (14.2 h; P = 0.76). Body weight (BW) did not affect MRT(iNDF) in reticulorumen and colon–rectum and total GIT MRT(Cr) (P ≥ 0.11). Reticulorumen and omasum MRT(Cr) increased as BW increased (P < 0.01), and abomasum MRT(Cr) decreased as BW increased (P = 0.02). Feed intake, and wet tissues and wet pool size of all GIT segments increased as BW increased, except abomasum wet pool size (P ≤ 0.01). The mechanism related to sex effect on MRT has to be elucidated. Reticulorumen MRT(iNDF) and total GIT MRT(Cr) were modulated by intake and capacity of reticulorumen and GIT, respectively. On the other hand, reticulorumen MRT(Cr) seemed to be regulated by reticulo-omasal orifice opening and saliva secretion.