Self-limiting supplements fed to cattle grazing native mixed-grass prairie in the northern Great Plains.

Objectives of this research were to compare animal performance with or without supplementation, compare effectiveness of three intake limiters, and to examine seasonal changes in nutritive value of native range in south-central North Dakota. Treatments included 1) control (CONT; no supplement); 2) hand-fed (HF) supplement, with no chemical limiter; 3) 16% salt (NACL); 4) 5.25% ammonium chloride and ammonium sulfate (AS); and 5) 7% calcium hydroxide (CAOH). Supplements were based on wheat middlings, barley malt sprouts, and soybean hulls and were formulated to provide 40% of the CP intake and 32% of the NEm intake of 350-kg steers. Trials 1 and 2 each used 70 yearling steers (370.8 +/- 0.04 and 327.9 +/- 0.76 kg initial BW for Trials 1 and 2, respectively). In each year, four 28-d periods from the latter half of June through mid-October were used. Steers were stratified by weight and allotted randomly to treatments in 1 of 10 16-ha pastures (two pastures per treatment for each trial). In Trial 1, diet sampling began in the first 28-d period, but supplementation did not begin until the second 28-d period. In Trial 2, supplementation and diet collection began in the first 28-d period. Cation-anion differences (DCAD; Na + K - Cl - S) for NACL, AS, CAOH, and HF supplements were 151, -735, 160, and 166 mEq/ kg, respectively. In Trial 1, no treatment, period, or treatment x period effects for supplement intake were detected (P > or = 0.29). In Trial 2, a treatment x period interaction for supplement intake occurred (P = 0.005) because HF steers were offered a constant amount of supplement daily, whereas steers fed AS, CAOH, and NACL were allowed to consume ad libitum quantities of supplement. Average daily gain in Trial 1 was not affected (P = 0.21) by supplementation. In Trial 2, NACL, AS, and HF treatments had higher (P < or = 0.07) ADG than CONT. In Trial 1, final weights were not affected by supplementation (P = 0.23). In Trial 2, final weights of NACL- and HF-fed steers were greater than for CONT and CAOH steers (P < 0.10). In Trial 2, CONT steer final weights were lower than all supplemented treatments (P < 0.10). For yearling steers grazing native range, use of NACL as a limiter resulted in increased weight gains compared with using either CAOH or AS; however, no limiter that was tested restricted supplement intake as effectively as HF. More research is necessary to determine the optimum limiter level and the effect of forage quality on supplement intake.