During weaning, methionine (Met) supply decreases as liquid feed is reduced and rumen function is developing. During this transition, calf starter should both promote rumen development and provide adequate nutrients postruminally. Rumen-protected forms of Met (RPM), and Met analogs, such as HMTBa or HMBi are used to increase Met supply, stimulate ruminal fermentation, or both. Our hypothesis was Met is a limiting AA and Met analogs might facilitate rumen development during this period. To test this hypothesis, 74 14 d old Holstein calves were individually housed from birth to 91 d of age, in 2 enrollment periods. Milk replacer (28% CP, 15% fat) was offered up to 1.6 kg DM/d. Calves were balanced for sex and randomly assigned to receive a control starter (CTRL, n = 20) or one supplemented with RPM (n = 16), HMTBa (n = 19), or HMBi (n = 19). Starters (23% CP, 2.5 Mcal ME/kg) were offered ad libitum and supplement inclusion was set to provide an additional 0.16% DM of Met equivalents. Weaning occurred from d 49 to 63. Body weight (BW) was measured weekly. Data were analyzed as a randomized block design with repeated measures over time, using enrollment period as block. Pre-planned contrasts were conducted against the CTRL. RPM and HMBi inclusion enhanced starter intake preweaning and HMBi tended to increase intake postweaning (Table 1). However, there were no differences from CTRL in postweaning BW or BW gain. Post-hoc contrasts among Met supplements indicated HMBi improved feed intake and BW gain postweaning (P < 0.05) with a tendency for greater final BW (P = 0.06). Table 1 (Abstr. 143). Effects of different forms of methionine or Met analogs¹ in Holstein calves

Item	Control	RPM	HMTBa	HMBi	SEM
Preweaning
Milk replacer intake, kg/d	1.37	1.35	1.38	1.37	0.02
Starter intake, kg/d	0.09	0.13*	0.09	0.12*	0.03
BW gain, kg/d	0.99	1.00	0.98	1.02	0.05
BW at d 49, kg	84.7	84.2	85.3	86.0	1.56
Postweaning
Starter intake, kg/d	3.27	3.20	3.05	3.40†	0.02
BW gain, kg/d	1.33	1.26	1.18*	1.42	0.07
Final BW, kg	133.2	130.2	129.5†	136.9	2.63

¹RPM = rumen-protected methionine; HMTBa = 2-hydroxy-4-(methylthio)-butanoic acid; HMBi = HMBTa isopropyl ester. Comparisons against control: *P < 0.05, †P < 0.1.